This article is from the Recreational Figure Skating FAQ, by Karen Bryden with numerous contributions by others.
Rocker is the curve of the blade from toe to heel, and is based on the
arc of a circle with a given radius. Thus, if you drew a circle with a
7 foot radius and placed a blade with a 7 foot rocker along the inside
curve of the circle, it would line up with the tracing, at least at
the rear (tail) of the blade. The curve at the front, behind the toe
pick is somewhat sharper. It is this difference of curvature which
allows you to turn and spin on the front of the blade.
The smaller the radius, the more rocker (amount of back and forth
rocking motion you can get when standing on the blade) it has. With
small radius blades, you can do turns with less chance of falling as
there is less blade on the ice. For the beginner, a 6' radius is fine
as, among other things, it is very forgiving in the toe pick
department -- you really need to lean way forward on them to catch the
The bigger the radius, the flatter the blade. This will generate more
speed as more of the blade contacts the ice. You will want a flatter
blade (7 foot or more) as you become more advanced. When you start
learning jumps, you will find that you need good edge control. Because
you have more blade on the ice, you can start to prepare your body
position for takeoff without falling off the edge so easily.