From the DMG
"Caster Level"
The power of the item (just as a spell’s caster level measures its power). The caster level determines the item’s saving throw bonus, as well as range or other level-dependent aspects of the powers of the item (if variable). It also determines the level that must be contended with should the item come under the effect of a dispel magic spell or similar situation.
For potions, scrolls, and wands, the creator can set the caster level of the item at any number high enough to cast the stored spell and not higher than her own caster level. For other magic items, the caster level is determined by the item itself. In this case, the creator’s caster level must be as high as the item’s caster level (and prerequisites may effectively put a higher minimum on the creator’s level).