What is THC-O?

Can someone explain what it is in dumbass terms please?

I got a cartridge that claims “Delta 8 enriched with THC-O”.

I know what delta 8 is, but not thc-o, or how it can enrich delta 8?

Update: I tried it what the fuck is this? This does not feel like weed im having minor hallucinations and just feel very weird. but its also like kinda good?