MSCD notes how in the U.S., traditionally exhibit is used to refer to a stand-alone document that’s attached to a contract, whereas schedule is used to refer to materials that could have been in the body of the contract but were moved to after the signature blocks.
An exhibit might consist of a form of noncompetition agreement that’s to be entered into at closing, or a copy of Acme’s articles of incorporation. A schedule might consist of a list of Acme’s pending litigation, or a list of Widgetco’s trademarks.
I know that other jurisdictions use other terminology. For example, I’ve been told that in Australia, annexure is used instead of exhibit.
I’d like to include in the third edition of MSCD an account of international attachments terminology, so I invite you to let me know in the comments what the practice is in your jurisdiction.