I also found this in the manual:

C. Casting - To cast the spell, click on the intended target, then click on the
spell icon in your memory
slot (or on the Hotkey Button if it you moved it there). A time gauge will
appear in the upper lefthand
corner of your screen, indicating the casting time. If the caster is struck or
moves during this time, the
spell can be interrupted, causing it to fail. The Channeling skill gives the
caster a chance of recovering
from such interruptions. Many casting classes do not get this skill until later
in their career, and the
chance of success is VERY small at the lower skill levels..

I knew there was a reason why I E-Mailed myself the manual.

Malkin
The gnome who thinks a little to much about EQ during work