The plain-English glossary I wish I'd had on day one

A few terms confused me far longer than they should have, so here's the version I'd hand my past self — no jargon: - Reconstitution — adding liquid to a freeze-dried powder so you can measure it. That's the whole word. - BAC water (bacteriostatic water) — water with a tiny amount of preservative so a multi-use vial stays usable for a while, vs. sterile/distilled which is single-use. - Subcutaneous vs intramuscular — into the fat just under the skin vs. into muscle. Different depth, different feel. - Half-life — roughly how long until half of a dose has cleared. It's about timing, not strength. - COA (Certificate of Analysis) — the lab sheet that's supposed to back up what's in a vial. What's a term that genuinely tripped you up at the start? Let's build the beginner glossary thread together.