Something that comes before a more important event or action that introduces or prepares for it. (Cambridge Dictionary)
An action or event serving as an introduction to something more important. (Oxford Dictionaries)
An introductory piece of music, most commonly an orchestral opening to an act of an opera, the first movement of a suite, or a piece preceding a fugue. (Oxford Dictionaries)
A short piece of music of a style similar to a prelude, especially for the piano. (Oxford Dictionaries)
The introductory part of a poem or other literary work. (Oxford Dictionaries)
An introductory performance, action, or event preceding and preparing for the principal or a more important matter. (Merriam – Webster)
You can describe an event as a prelude to a more important event when it happens before it and acts as an introduction to it. (Collins Dictionary)
Meaning of prelude. Word pandit.
Prelude is an introduction to something else in short before that actual event or action.
Prelude and Postlude.