Caster level

From NWNWiki

The caster level of a cast spell is a measure of the power of that particular casting. For spells cast from items, this number is given in parentheses after the relevant item property. For spells cast by a character, the caster level is the character's level in the class used to cast the spell. (Epic spells cast from items are an exception in that their caster level is not given in parentheses. The caster level for most default epic spell item properties is 25, with the exceptions being epic warding and hellball, for which the caster level is 30.)

In the event that a class feature, domain granted power, or other special ability provides an adjustment to a character's caster level, that adjustment applies not only to spell effects (such as duration and damage) but also to the check to overcome spell resistance and to dispel checks. On the other hand, level drain effects and/or spells could cause a character's caster level to decrease.
Note: A common misconception is that pale master levels add to caster level. They do not.