Generally Accepted Accounting Principles (GAAP) are the rules that govern how accountants measure, process, and communicate financial information to ensure consistent accounting procedures are followed. The key concepts of GAAP include the business entity concept, continuing concern concept, time period concept, consistency principle, conservatism principle, objectivity principle, materiality principle, monetary-unit concept, full disclosure principle, cost principle, revenue recognition convention, and matching principle. These concepts provide the framework and guidelines for proper accounting of financial transactions and reporting.