ROCKER:
The rocker is the curve through the length of the board.
If you put the board on the ground slick down the board will rock if you
tap it on the nose or tail.

Dead flat means it will lie flat with the gradient shaped into the nose
the only thing coming off the ground. It will not "rock" This is fast and
holds in well, More for the advanced rider.

Little bit of nose rocker means it will have a slight lift off the ground
from around the first foot or so from the nose. Less Likely to Nosedive
and easier to turn. For the Intermediate Rider.

Quite a lot of rocker means both the nose and tail will be lifting off the
ground if it's lying on the ground. Only the middle of the board will be
touching the ground.
Not likely to nosedive and easy to turn but not very fast or responsive.
For the Beginner rider

Touch of reverse rocker means the nose and tail will be touching the
ground and there will be a slight lift off the ground in the middle of the
board.
This board is super fast and responsive but easy to catch rails and nosedive.
For the Advance rider or pro

Most boards are Dead Flat. Most Pro's ride Reverse rocker.
Hope this answers your questions.
Here's the link for boards:
http://www.bodyboardking.com/c/21636/1/bodyboards.html
Thanks Toby