The problem with wanting a more specific definition is severalfold:
1. Even the best researchers don't yet know what specifically causes people to be autistic.
2. When they do end up getting a clue what makes all autistic people autistic (if there is such a thing), it's bound to be only describable in arcane professional language that nobody would understand. Because if there is one thing that causes all the different manifestations of autism, then it's likely not going to be something specific and concrete, but rather a "root" set of traits that are abstract-seeming and only make sense in neurology-speak. (For instance one single underlying trait that can cause seemingly opposite sets of autistic traits.)
3. When you do get into the more concrete things that can be described in a single sentence, then you're only describing the experience of one type of autistic people, not many types.
So that's the reason that when you want a description that fits all autistic people, it's going to be broad and general like that. There's no easy way of saying what we do have in common. You're asking for something that even the people with the most data about autism of anyone, even they don't have it.
But then judging from the responses you're getting on this thread, many of them certainly don't describe my form of autism. So why don't I just make up a sentence that describes my form and not necessarily theirs? It'll be the same level of accuracy as the ones who go on about it being primarily a social condition. But I have a feeling more people will object, both because my form of autism (i.e. the traits I have that result in me being diagnosed as autistic) isn't the most common, and because most people just assume the professionals are right and that what we all have in common is crappy social skills. So here's my own heavily biased, subjective, and individual definition of autism, which is the only possible way I can give you more concrete information than what I gave before.
Autism involves tendencies towards experiencing patterns of sensory information rather than using idea-based thought, initially learning language as repeating strings and patterns of sounds rather than words, hearing the tonality, rhythm, and music of people's voices rather than hearing their words, noticing the patterns of people's movement more than remembering their faces, having abilities that are constantly shutting down or shifting in and out, having difficulty finding your body and moving it once you find it, having trouble deliberately starting/stopping/shifting/combining/etc. movements or thoughts or memories or words but at the same time being very good at such things if it's triggered or automatic instead of voluntary, having one's speech so dominated by echoing things you've heard and forming plausible but potentially inaccurate sentences rather than expressing your thoughts that it's completely useless, learning things over and over and not having them stick because they all depend on building blocks that you have to set up every single time rather than having them stay in place, frequently being so flooded with sensory data that you become completely overloaded especially in less familiar situations, having sensory data be so intense and brain-flooding that it becomes fragmented and confusing, having great difficulty putting things and experiences into categories to the point where you can't easily recognize and interpret the meaning of these sensations and experiences, trouble exerting control over your thoughts and movements, moving in repetitive and unusual ways in order to modulate sensory information and comprehend one's surroundings and interact with those surroundings, and all the potential results of these differences singly and in combination.
There. That described many of the particular ways that an autistic person can have differences in perceiving, thinking, and reacting to their environment. However these are the particular ways that apply to only one set of people. There is no simple way to be particular and universal at the same time when it comes to describing autism. But the above things are why I meet the criteria for autism, and why people similar to me do, even though we're seemingly not a majority of autistic people. There's reasons I didn't mention social skills, because it's not so much that I'm missing a social module in my brain (as far as anyone can tell about their own brain), but rather that all these differences in perception/thought/action can result in social difficulties when faced with a person who perceives and responds to the world very differently. (Just as that person has social difficulties with someone like me.) And things like that. To me social skills are way the heck out on the periphery of things I care about that are affected by being autistic in some way.
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"In my world it's a place of patterns and feel. In my world it's a haven for what is real. It's my world, nobody can steal it, but people like me, we live in the shadows." -Donna Williams