DEFINITION of 'Generally Accepted Accounting Principles-GAAP'. The common set of accounting principles, standards and procedures that companies use to compile their financial statements.GAAP are a combination of authoritative standards (set by policy boards) and simply the commonly accepted ways of recording and reporting accounting information.Next Up.ow is market to market (MTM) treated under Generally Accepted Accounting Principles ... Mark to market accounting became a part of generally accepted accounting principles, or GAAP, in 1993 when Statement of Financial ...