Legal Definition
A condition is a provision in a contract or legal instrument that makes the existence of a duty or the performance of an obligation dependent upon the occurrence or non-occurrence of a specified future event. If the condition is not satisfied, the party whose performance was conditioned is typically excused from that obligation.
Plain-English Translation
Think of a condition like a rule in a game that says 'you only get the prize if you finish the race.' In law, it is a requirement that must happen before someone is officially forced to do what they promised, like paying money or delivering goods.