if[Not][UnitId]Has{Buff,Debuff}Title[{<,=,>}XX]=<buffTitle1>[,<buffTitle2>,...]
where XX refers to the number of buff/debuff applications,
e.g. ifTargetHasDebuffTitle<5=Sunder
and <buffTitle> is the full name (including capitalization and spaces) of the buff/debuff title as it appears in the tooltip.
To check for buff categories like DoTs, immobilization, etc. use ifUnitIs.
Also see ifUnitHasBuff.
Legend
<item> is a placeholder and the entire string including <> should be replaced with the appropriate value. [text] means text is optional. {option1,option2,option3} means one of option1, option2 or option3 must be chosen. Batteries not included. UnitId can be any valid UnitId sequence as described in http://www.wowwiki.com/UnitId. Capitalization of UnitIds is not important. e.g. player, pet, target, targettarget. If the UnitId is optional, player is assumed.