Definition:

Acceptance Testing (often referred to as User Acceptance Testing or UAT) is a level of software testing conducted by end users, stakeholders, or the client to verify that the system meets the agreed-upon Acceptance Criteria and business requirements. It is the final validation step before the product goes live.

Example:

After building a new e-commerce platform, Acceptance Testing might involve actual users placing orders in a test environment, confirming that shipping costs are calculated correctly, and verifying that order confirmations are sent to the correct email addresses