Quality Assurance (QA) - the professional term for testing
Bug - A software problem that exists at the implementation-level (i.e., only exists in source code)
Flaw - A software problem at a much deeper level, particularly in the design, which likely bleeds into the code level as well
System testing - Test the individual game components; primarily done internally, within development team
Play testing - Primarily done among development team, product and marketing managers
Alpha - Refers to the fact that everything has been implemented, but there are many bugs and gameplay/functionality issues; testing audience widens to senior-level personnel in company
Beta - Refers to the fact that everything has been implemented, and many critical gameplay/functionality issues and bugs have been resolved (but there are small bugs still lingering); even wider audience, nearly public