Definitions for "French overture"
a somewhat saucy piece of music which starts with slow dotted rhythms and suspenders, which give way to a fast (farce sic) fugal section where all the instruments chase each other with the same tune
Baroque form favored of the French composers and their imitators that describes the kind of movement that begins stage works and instrumental suites of the period. There is a slow, pompous introduction often involving dotted rhythms, an imitative, sometimes fugal Allegro, and at the end a return to the dotted style of the opening. The traditional explanation is that the king would take his place during the pompous beginning. Familiar examples are the overture to Handel's Messiah and the first movements of the Bach Orchestral Suites. Handel's Music for the Royal Fireworks begins with a French-ish overture, though the Allegro is not imitative. Have a look.
a two-part piece, the opening movement of a larger work such as an oratorio, suite, or opera. Called "French" because it developed primarily in the late-17th century works of Jean-Baptiste Lully and his successors. The opening movement is majestic, slow in tempo, and marked by dotted rhythms. Following this is a faster movement, usually imitative in texture. Often, the opening slow section returns briefly to close out the entire movement.