As others indicate, "unschooling" can mean pretty much anything from overt neglect through various forms of benign neglect or child-led topic selection, all the way through eclectic homeschooling.
Most of my hard-core unschooling friends lean a little too far toward the former for our personal tastes and pedagogical philosophy, but it clearly works for some parents and some children.
They tend to believe (as a philosophy) that anything that a child has a need to learn, that child will be most receptive and learn that thing/skill fastest when s/he sees a need to do so. That is, motivation is inherently intrinsic, and anything which lacks that intrinsic motivation is not really learning in the first place.
(I don't say that I completely agree with this as a governing philosophy for educating children, by the way, but it is what my friends who unschool truly believe.)
That said, I tend to think rather strongly that there are some foundation skills that don't seem all that useful in and of themselves, and which few children are intrinsically motivated to master... but which make higher learning later pretty easy by comparison with those who DID NOT master them.
