Meanings of brief prologue in English

I wrote a brief prologue to the play, and wrapped in a red scarf, I proudly read it to the sold-out audience.

The bulk of the action, after a brief prologue showing a judicial execution, takes place in 1965 in an Oldham pub belonging to Harry Wade.

After a brief prologue in Tangier (you suave beatniks), the couple come together in the most suitable of American cities: the deserted, undead Detroit.