What Is Autism?

My best friend (who is neurotypical) asked me this question a few days ago.  She asked me: "What exactly is ASD?"
She knows I have ASD (Autism Spectrum Disorder) and she knows that makes me Autistic.  But what she did not know is how autism works or, more precisely, what makes an Autistic different from a neurotypical.
Autism is hard to explain.  I've heard advocates use the term "puzzle" to describe autism, as if it's something complex and challenging that we can't quite quite figure out but are compelled to work at, over and over again, until we can unlock its secrets.  I've heard discussion among specialists about neurotransmitters and anomalies in brain structure.  I've heard about the behavioral and sensory challenges that are often associated with Autistics.  I've heard drabble about "low-functioning" and "high-functioning" Autistics and Autistics who are referred to as "savants."  I've heard about non-verbal Autistics and verbal Autistics, Autistics who excel at math and science, and Autistics whose passion lies in language.  Autism is different in everybody.  And I am not an expert in everybody.  In fact, I am far from it.  But I'd hazard to guess that I am an expert in myself.
I ended up telling her that autism means that my brain works, on a fundamental level, a little bit different than hers.  I said that autism makes me see things differently and think about them in a different way.  I said that, even though we both live in the same environment, my "world" is just a little bit different than hers.
I don't know what it is like to be neurotypical, but I do know this; I see things just a little bit differently than neurotypicals do, and I am perfectly content with that.