prolegomenon

A preliminary discussion, especially a formal essay introducing a work of considerable length or complexity.

Prefatory remarks or observations.

A preliminary observation: chiefly used in the plural, and applied to an introductory discourse prefixed to a book or treatise.

A preliminary remark or observation; an introductory discourse prefixed to a book or treatise.

A prefatory discussion; a formal essay or critical discussion serving to introduce and interpret an extended work.

a preliminary discussion inserted at the beginning of a book or treatise