An overture is a piece of music played by an orchestra at the beginning of an opera or play. When an overture begins, the actors take their places and wait for the curtain to rise.
The noun overture can also mean "a suggestion or approach designed to get a reaction." Your romantic overture of singing to your girlfriend in the restaurant was met with an embarrassed stare. An overture can also be an event that comes first, like your story about how the after-school program has helped hundreds of kids, an overture to the plea for donations you made next.