What is the difference between validation and verification?

Validation is the process of confirming that a software product meets user expectations and requirements specifications. The answer to the question: "Are we building the right product?". It is conducted at later stages of development, usually after integration or at acceptance testing.

Verification is the process of checking that the software product is created in accordance with the specifications, meaning the functionality is correctly implemented according to the design and requirements. The answer to the question: "Are we building the product correctly?". It can be performed at all stages of the development lifecycle (requirements review, unit testing, integration testing).

Key differences:

Characteristic	Validation	Verification
Goal	To check compliance with customer/user expectations	To verify compliance with specifications
Who conducts	Customer/User, Testers	Testers, Developers
When conducted	After development/integration completion	At all stages of development
Main question	Are we building the right product?	Are we building the product correctly?
Methods used	Acceptance testing, UAT, requirements-based testing	Code review, static analysis, unit testing, integration testing

In simple words: Verification checks whether we have correctly implemented what we were supposed to build (according to the technical specifications), and Validation checks whether we have correctly implemented what the user actually needs.