Learn in the textbookValidation, Acceptance, and Migration
DefinitionAcceptance testing (受入れテスト) is led by the ordering party (the users), who use the delivered system under conditions close to real operation to decide whether to accept it.
ExplanationIt takes place before formal sign-off (検収, checking the delivered goods and taking them over), and confirms that the functions specified at the time of ordering are all present. The order in the figure is typical of cases where the contractor handles everything up to system testing.
AnalogyIt is like collecting a bicycle from the repair shop: you listen to the explanation, ride it yourself, and pay only once you are satisfied.
Memory hookThe one who decides whether to accept is the one receiving the goods, so the name itself tells you who does the test.