Neurotypicals are generally assumed to have certain qualities in common, including strong social and communication skills, a lack of sensory issues, and an ability to navigate new or socially complex situations. Naturally, this assumption isn't universally accurate: plenty of people without diagnoses are shy, nervous, prefer routine, are upset by loud noises, etc.
The term neurotypical is also the forerunner of another even newer term, "neurodiversity." The neurodiversity movement is built around the idea that autism spectrum disorders (as well as other developmental differences such as ADHD) are not disorders to be treated but differences to be respected. Members of the neurodiversity movement are often opposed to the idea of a cure for autism.