It is a different form of brain wiring that often manifests itself in psychological disorders or even special talents. It is described as a spectrum because it can show up with no rhyme or reason,going from the profoundly non-verbal autistic that require full support to live to what can be considered higher functioning that can include the subset of autism described as Asperger's Syndrome where there are no major cognitive delays or a lack of speech during early childhood,but social impairments and a slew of what is described as co-morbid conditions such as depression and OCD.
Overall,a diagnosis is a subjective process that is all up to the clinicians to decide if you meet the impairment levels to give you your tag.
We all share common traits from time to time,but also vary so much that no two of us are ever the same,much like two humans that are considered neurotypical. At time,we use the tern neurodiverse to describe ourselves.