When I was young, "autism" was seen as a severe and generally debilitating mental disorder, and "Asperger's syndrome" was known as an affliction with similar but less dramatic symptoms. When the two were folded together into "Autism spectrum disorder", it was quite natural to understand this as a declaration that "autism" was not a singular condition but a trait you might have more or less of, that what we had previously called "Asperger's" was just "autism" in a less severe form, and that the "autism spectrum" described the amount of autism you had, ranging from none to a great deal. This is still supported in pop psychology by are-you-autistic questionnaires yielding a numeric score, and it was always kind of baked into general discussion of autism by Hans Asperger's original "extreme male brain" theory.
I must confess that I cannot make any sense of autism anymore, under the multidimensional-multi-spectrum definition used in this article; it seems to be all kinds of different things, or none of them, and I have no idea what it is that different people who have autism are supposed to have in common, such that the same term ought to be used to describe them. The only concrete idea I can find in the concept of "autism" now is the proposition that different people's minds work differently, which I would have taken to be obvious. Of course this is all very far from any area in which I may have expertise.