A reference document, compiled by a copy editor, to show editing decisions that have been made and to ensure those decisions are applied consistently throughout the text.
Style sheets are an important tool for achieving consistency, and are used by all professional copy editors.
Some items typically included in a style sheet are: choice of dialect (e.g. Canadian versus American English); spelling and proper use of invented words; a list of character and place names; and punctuation and grammar choices.
In independent publishing, a copy editor or service provider should be able to provide the client with the style sheet upon request.