You are good at acting, misleading, and lying.
Check: a Bluff check is opposed by the target's Sense Motive check. You can also use Bluff to feint in combat, create a diversion to hide, or deliver a secret message (all as per the Bluff skill description in the 3.5 PHB).
Synergy: 5 or more ranks in Bluff gives you a +2 bonus to Diplomacy, Intimidate, and Sleight of Hand checks, as well as on Disguise checks made when you know you're being observed and are acting in character. Conversely, 5 or more ranks in Translate gives you a +2 bonus to Bluff checks made using the Trick Magic Device feat involving written arcane magic. These bonuses increase by +1 for every additional 10 ranks (that is, +3 at 15 ranks, +4 at 25 ranks, and so on).
Feat: the Improved Feint feat allows you to use this skill to feint in combat more quickly (as per the Improved Feint feat in the PHB), while the Trick Magic Device feat allows you to use this skill to activate spell completion, spell trigger and command word magic items that you usually could not use (as per the Use Magic Device skill in the PHB).