The notion of mood in grammar refers to information conveyed by special verb forms regarding the speaker's desires, certainty, or opinion regarding a fact. The main categories for mood in French are the subjunctive, e.g.: Il faut que tu fasses and the conditional, e.g.: je voudrais partir (one could also include the imperative and the interrogative in this category).
Like tense, information regarding mood in indicated on the verb by stem changes and suffixes.