Basics

An abrreviation for Polytetrafluoroethylene
Sold Under the Brand Name Teflon
An Engineering Plastic
A Floropolymer that is highly chemical resistant, and has low friction
Hard to work with, but it can be SLA Printed or Chemically coated on materials
Useful for chemistry equipment, medical equipment, nonstick coatings, and low friction componets

Safety

TLDR: Not the WORST (ie on a scale from Deionized Water to Dimethyl Mercury / or Sulfur Mustards (ie critical to life + benign TO toxic and no real use) it's probably a 4) but not the best and tied to some VERY NASTY related/required chemicals so best to avoid it if possible ( Reduce / Substitution / Precautionary Principle etc)
- Also special note that as with the Canary in the Coal Mine , at high temperatures "Teflon Coated" / Nonstick Pans release some "nasties" that aren't bad enough for humans (at least in the Acute sense), but ARE lethal to Birds and such, so be careful about that
For a pretty good communication of the state of current understanding, the videos (linked under this page's external links section) by Veritassium (YouTube Channel) and Adam Ragusea (YouTube Channel)
- TLDW is PTFE is mostly fine, PFAS though are gnarly, ESPECIALLY Occupational Exposure
  - So manage exposures + be careful on that, but most "average joes" are alright

Forever Chemicals
- (PTFE is considered one, along with PFAS and others)
Fluoropolymers
- The family of Polymers PTFE Falls into, along with ETFE and Fluoroelastomers