THCa

THC before it is heated. It is the big number on most flower labels; heat (a flame, a vape, an oven) turns most of it into THC.

Related terms

THC
Delta-9 THC in its active form, already converted before any heat. On raw flower it is usually a small number sitting next to a large THCa.
Total THC
What the label works out you actually get: THCa converted, plus any THC already there.
Diamonds
Crystals of THCa grown out of a concentrate, usually sold in the terpene-rich liquid they grew in, called sauce. The crystals themselves test close to pure THCa.