What is a lane?

I would like the documentation to clearly explain what a `lane` is, what the ruby DSL for a `lane` is, along with the `desc` command and other commands that can possibly be run around a `lane`. Clearly differentiating between what a `lane` can do as opposed to a standard Ruby function would be nice.

There is documentation on a `private_lane`, but that seems to assume people know what a `lane` is to begin with.

I feel like these are the sorts of things that should at least be in the FAQ of the documentation, if not in a "Fastlane 101" sort of section that explains what things are.