Failure of an express condition
An event, not certain to occur, which must occur, unless occurence is excused, before a duty to perform arises. A condition limits or modifies duties created by other contract language; a condition does not create an independnet obligation. Look for words like "if," "as long as," "when," "provided that," "on condition that." and "unless."
Strict compliance is required but it does not create an independent legal obligation.