To me it means basically the freedom to learn what is relevant to your life, in your own way and in your own time. Schools interfere with this process. Hence, "un"schooling.
Here is an excellent definition:http://www.midnightbeach.com/hs/Unsc...Undefined.html
In some ways, all homeschooling is unschooling -- we don't isolate our kids from life, or move at the sound of a bell, or require permission slips, or neglect the individuality of our children. Where unschoolers differ from other homeschoolers is the extent to which we let children be responsible for their own education.
Unschoolers believe that the natural curiosity of a healthy child, given access to a rich environment, will lead the child to learn what he or she needs to know. When learning comes about as a result of the child's desires, it is absorbed easily, enthusiastically, openly. The child works harder because he is doing what he thinks is important, rather than what someone else has told him is important. New knowledge starts with a context because it fits in with things the child already cares about. Learning driven by real desire is so much more efficient than passive absorption that unschoolers can tolerate much more exploration, dabbling, dawdling and play than can curriculum- inflictors. The unschooling literature abounds with stories of children who paid no attention to math or reading for their first ten years and then caught up in just a few weeks.
When learning is imposed from without, there are many deleterious effects. The child may not be ready for the material or may be beyond it; the child may resist it, either because he has something better to do or just out of general orneriness. When you force a topic, you short-circuit precisely the volitional parts of the mind that are critical to real learning. You may produce memorization, but cannot effect understanding. You risk the child developing a dislike for the topic, for the teacher, and even for learning itself.
Child-driven learning is fundamentally active. Children are doing things because they have taken responsibility for carrying out the actions needed to fulfill their desires. Unschooling is centered around the idea of learning, with the student as the center of action and the source of activity, rather than on the idea of teaching (with the teacher as the center of action and the source of activity). Not only does this make the learning more effective, but it encourages the child to develop virtues: independence, self-reliance, and a sense of responsibility. The child learns that if he wants something to happen, he has to make it happen.