The surface of the ball "reads" the surface of the lane. Basically, it looks for friction. A ball that is not "reading" the lane isn't finding any (enough) friction.
A ball that reads early is finding friction in the front part of the lane, the first 20-30 feet. If it's finding friction there, it's hooking there, which means it probably isn't going to have energy left to hook later. Early read is usually Bad (tm). Not always, but usually.
A ball that reads late is usually looking over its anthropomorphized shoulder at what was supposed to be the breakpoint. Also usually Bad, but not always.
The usual idea is that the ball reads the 30 feet through the end of the pattern, the midlane. It begins to find friction there, with the amount of friction increasing downlane. This friction makes the ball hook.
A lot of midlane read gives a very smooth reaction, there is not usually as much hook in the backend. Very little midlane read means the ball doesn't find enough friction until it exits the oil pattern and reacts strongly off the dry.
SH
