Glossary of FDA and biotech catalyst terms

Short definitions of the terms that come up in the tracker, in company filings and in our guides. Where a term has a guide of its own, the definition links to it.

Accelerated approval: An FDA approval based on a surrogate endpoint that is reasonably likely to predict clinical benefit, for serious conditions with unmet need. The company must run confirmatory trials afterwards, and the indication can be withdrawn if they fail. See expedited programmes.
Advisory committee (AdComm): A panel of outside experts that holds a public meeting to advise the FDA on an application. Its vote is not binding. See what happens at an advisory committee meeting.
ANDA: Abbreviated New Drug Application: the route for a generic copy of an approved small-molecule drug. See NDA vs BLA.
BLA: Biologics License Application: the application to market a biological product such as an antibody, vaccine, or cell or gene therapy. See NDA vs BLA.
Breakthrough Therapy designation: An FDA designation for drugs whose early clinical evidence suggests a substantial improvement over existing treatment for a serious condition. Brings intensive FDA guidance during development; doesn't change the approval standard.
CBER: The FDA's Center for Biologics Evaluation and Research, which reviews vaccines, blood products, and cell and gene therapies.
CDER: The FDA's Center for Drug Evaluation and Research, which reviews NDAs and most therapeutic biologics such as monoclonal antibodies.
CMC: Chemistry, manufacturing and controls: the part of an application covering how a product is made, tested and kept consistent. A common source of CRL deficiencies.
Clinical hold: An FDA order stopping or delaying a clinical trial until safety or other concerns are resolved.
Complete Response Letter (CRL): The FDA's letter saying it can't approve an application in its current form, listing the deficiencies. Since 2025 the FDA publishes these letters. See what a CRL means.
Confidence interval: The range within which a trial's true effect plausibly lies, usually at 95% confidence. A narrow interval well away from zero (or from 1, for a ratio) is a firmer result than a wide one.
Database lock: The point after a trial's last visit when the data have been cleaned and are frozen for analysis. Topline results usually follow within weeks.
Day 74 letter: The FDA's early communication on a newly filed application, flagging any review issues found so far and the planned review timeline.
Data monitoring committee (DMC): An independent group that reviews unblinded trial data while the trial runs, and can recommend stopping it for benefit, futility or safety. Also called a DSMB.
Endpoint (primary and secondary): The measurement a trial uses to judge whether a drug works. The primary endpoint is the one the trial is designed to test; secondary endpoints are supporting measures, usually tested in a fixed order. See how to read a topline readout.
Form 8-K: The SEC "current report" a US company files to announce a significant event, usually within four business days. Most catalyst dates on this site come from one. See 8-K vs 6-K vs press release.
Form 6-K: The report a foreign private issuer furnishes to the SEC with information it has made public elsewhere. The foreign-company counterpart of the 8-K.
EDGAR: The SEC's public database of company filings, free to search. See how to verify a date on EDGAR.
Exhibit 99.1: The attachment to an 8-K or 6-K that usually holds the press release itself.
Fast Track designation: An FDA designation for drugs addressing an unmet need in a serious condition. Allows more frequent FDA meetings and a rolling submission.
Form 483: The list of observations an FDA inspector hands over at the end of a facility inspection. Unresolved observations can lead to a CRL.
Hazard ratio: For time-to-event endpoints, the rate of the event on the drug relative to the comparator. A hazard ratio of 0.70 means about a 30% lower rate at any given time.
IND: Investigational New Drug application: what a company files with the FDA before testing an unapproved drug in people.
Interim analysis: A pre-planned look at trial data before the trial ends, usually by a DMC. "Continue as planned" is not a positive efficacy result.
Major amendment: A substantial submission of new information during an FDA review. The FDA can extend the PDUFA date by three months to review it.
NDA: New Drug Application: the application to market a new drug, usually a small molecule. See NDA vs BLA.
New molecular entity (NME): A drug whose active ingredient the FDA has never approved before. NMEs and original biologics are reviewed under the PDUFA "Program", with a review clock that starts at the 60-day filing date.
Open-label: A trial where patients and investigators know who's receiving which treatment. Faster and simpler than a blinded trial, but more open to bias.
p-value: The probability of seeing a result at least this extreme if the drug truly had no effect. A small p-value says chance is unlikely; it says nothing about how large or useful the effect is.
PDUFA: The Prescription Drug User Fee Act, under which companies pay application fees and the FDA commits to review timelines. Renewed every five years. See what a PDUFA date is.
PDUFA date (target action date): The date by which the FDA aims to act on a specific application. Not published by the FDA; disclosed by the company. The FDA can act early, extend it after a major amendment, or occasionally miss it.
Phase 1, 2, 3 and 4: The stages of clinical development: safety and dosing, early efficacy, confirmatory trials, and studies after approval. See clinical trial phases explained.
Pivotal trial: A trial designed to provide the main evidence for approval, usually Phase 3. Also called registrational.
Placebo-adjusted: The drug's effect minus the placebo group's effect, which is the honest measure of what the drug added.
Priority Review: A designation, decided when the FDA files an application, that shortens the review goal from 10 months to 6.
Refuse to file (RTF): The FDA declining to review an application, within 60 days of receipt, because it's incomplete. The company has to fix it and resubmit.
Regulation FD: The SEC's fair-disclosure rule: when a company shares material information outside the company, it must make it public to everyone, not just selected investors or analysts.
Resubmission (Class 1 and Class 2): A company's response to a CRL. Class 1 covers minor items and has a 2-month review goal; Class 2 covers everything else and has a 6-month goal.
RMAT designation: Regenerative Medicine Advanced Therapy: the cell- and tissue-therapy counterpart of Breakthrough Therapy designation.
Rolling submission: Submitting completed sections of an NDA or BLA as they're ready, available to Fast Track products. The review clock starts when the final section is in.
Serious adverse event (SAE): A side effect or medical event during a trial that is life-threatening, causes hospitalisation, disability or death. A regulatory category, not a judgement of severity.
sNDA / sBLA: A supplemental application to change an approved product's label, for example to add a new indication. Efficacy supplements get their own PDUFA dates.
Standard review: The default FDA review goal: 10 months, measured from the 60-day filing date for new molecular entities and original biologics.
Surrogate endpoint: A measurement, such as tumour shrinkage or a lab value, used in place of a clinical outcome like survival because it's expected to predict it. The basis for accelerated approval.
Treatment-emergent adverse event (TEAE): Any adverse event that starts or worsens during treatment in a trial, whether or not the drug caused it. Compare rates between drug and placebo groups.
Topline data: The first high-level results of a trial, usually the primary endpoint, key secondaries and a safety summary, released before the full dataset.
Type A meeting: A meeting with the FDA for a programme that has stalled, often requested after a CRL. The FDA aims to hold it within 30 days of the request.

More guides

What a PDUFA date is, and why the FDA doesn't publish themThe PDUFA target action date is the FDA's own deadline for deciding on a drug application. Here is where it comes from, how it moves, and why you only hear about it from the company.
What happens at an FDA advisory committee meetingWho sits on an FDA advisory committee, how the day runs, what the vote means and doesn't mean, and where to find the documents beforehand.
What a Complete Response Letter means, and what usually followsA Complete Response Letter is the FDA's "not yet" on a drug application. What it contains, the company's options, how resubmission clocks work, and how to read the announcement.
How to read a Phase 3 topline readoutEndpoints, p-values, effect sizes, safety tables and the phrase "met its primary endpoint": a practical guide to reading the press release a company puts out when pivotal trial results land.
Clinical trial phases explained: Phase 1 to Phase 4What each phase of clinical development is for, roughly how big the trials are, what the in-between labels like 1b, 2a and 2/3 mean, and what a readout at each stage can and can't tell you.
NDA vs BLA: the two kinds of US drug applicationWhy some products are filed as a New Drug Application and others as a Biologics License Application, who reviews each, what supplements and rolling submissions are, and why the difference matters after approval.
Fast Track, Breakthrough, Priority Review and Accelerated Approval explainedThe FDA's expedited programmes are often lumped together, but they do different things at different stages. What each one is, what it changes about the timeline, and what it doesn't promise.
How to verify a catalyst date yourself on SEC EDGARA step-by-step walkthrough of the method behind this site: finding the filing that announced a PDUFA date or readout window, reading it properly, and spotting the traps that catalyst calendars fall into.
8-K vs 6-K vs press release: where catalyst dates are disclosedWhy almost every row on this site links to an 8-K exhibit, what the 6-K is for, when a press release has no filing behind it, and how the item numbers and "furnished vs filed" affect what you're reading.
Why catalyst windows like "H2 2026" are vague, and how they narrowMost biotech catalysts don't have a date, only a window the company guided to. Why that is, what the common phrases mean, how windows tighten or slip, and how this site handles them.