In music, the introduction is a passage or section which opens a movement or a separate piece. In popular music this is often called an intro.
The introduction may be the first statement of primary or other important material, may be related to but different from the primary or other important material, or may bear little relation to any other material.
In an essay or article, an introduction is a beginning section which states the purpose and goals of the following writing. This generally followed by the body and conclusion, and may be preceded by an abstract.