In grammar, the subjunctive mood is a verb mood typically used in dependent clauses to express wishes, commands, emotion, possibility, judgment, opinion, necessity, or statements that are contrary to fact at present. It is sometimes referred to as the conjunctive mood, as it often follows a conjunction. The details of subjunctive use vary from language to language.
So, you'd say things like, "if I were a painter, I'd probably die from lead poisoning." Even though "were" isn't the proper tense for the subject, "I," you use "were" to indicate that what you're talking about hasn't happened.