I've seen both terms "Overture" and "Ouverture" being used to designate the intro or first part of a multi-part composition. For instance, we have:
- Lully's Roland begins with an Ouverture,
- Bach has a lot of works whose first element is an Overture,
- Overture - "An instrumental composition intended especially as an introduction to an extended work",
- Overture - "Overture in music is the term originally applied to the instrumental introduction to an opera".
Which is the correct term to use to designate the first part of a multi-part piece?