Someone who's neurodiverse has a brain that doesn't work in a typical way. It's common to describe someone with autism spectrum disorder as neurodiverse.
People's brains function in widely different ways, and the etymology of neurodiverse reflects that fact: it comes from neuro-, "pertaining to the nervous system," and diverse, "differing from one another." Someone who's neurodiverse has neurological differences from the average person. This might mean they have difficulty communicating or using language; or that they have a learning disability or an attention disorder.