Tetrahydrocannabinolic Acid (THC-A) is the precursor cannabinoid to THC. The cannabis plant generates a wide range of cannabinoid compounds in their acidic versions throughout its natural growth cycle. Once the plant is put through a decarboxylation process, these acidic versions become the non-acidic versions of the cannabinoids you might be most familiar with like CBD and THC.
THC-A is a non-psychoactive cannabinoid but it can be easily decarboxylated at lower temperatures than other cannabinoids. Which makes it very difficult to find THC-A cartridges, THC-A edibles, and other THC-A products. Some of which you can find right here.