The subjonctif is a mood in the French language used to express doubt, emotion, necessity, or uncertainty. It often appears in dependent clauses introduced by specific conjunctions or verbs that convey these feelings. For example, phrases like "Il faut que" (It is necessary that) or "Je souhaite que" (I wish that) typically require the use of the subjonctif. In terms of conjugation, the subjonctif has its own set of endings, which differ from the indicative mood. Regular verbs follow specific patterns, while irregular verbs may have unique forms. Mastering the subjonctif is essential for expressing nuanced thoughts in French.