Def 1: (linguistics) To possess a pattern of vocabulary, syntax, and scansion that indicates an autistic speaker or writer; usually but not always includes failure to comprehend sarcasm, rhetorical questions, and other benignly deceptive linguistic devices.
The above definition tisms like whoa because the person who submitted it literally used the Merriam-Webster format.
A term used ironically as self-deprecating humor by individuals on the autism spectrum as a way of reclaiming their identity from being pathologized. The use of the term makes autism sound like an antiquated, old-timey disease, reflecting society's biases against neurodivergent folks back at them.
"You'll have to forgive me for acting so awkward around your friends.... my 'tism was acting up, sorry!"