THCa is a cannabinoid that’s found naturally in hemp and marijuana plants. THCa turns into Delta-9 THC when you add heat. This process is also known as decarboxylation. You probably already know all about decarbing flower — it’s what you do when you smoke, vaporize, or make edibles.
That’s also why eating raw flower won’t get you high, but smoking it or baking it into brownies will. Raw flower is super high in THCa.