What is the subjunctive in French?

It is a tense to express a doubt or a wish such as "I wish it were sunny."

It's constructed in the present tense by taking the 'Ils' form, removing the ending and adding e, es, e, ions, iez, ent.

It isn't used when this wish is in future, ie. "Il dit que le train va être en retard", in this case it is reported speech in the present.