Verification is the process of confirming whether software meets it specification. It typically involves reviews and meetings to evaluate documents, plans, code, requirements and specifications. This can be done with checklists, issue lists, walkthroughs and inspection meetings.
Validation is a process of confirming whether software meets user's requirements. It involves actual testing and takes place after verifications are completed.
[Software Testing and Quality Assurance published by Nirali Prakashan]
Verification: The process of determining whether the products of a given phase of the software development process fulfill the requirements established during the previous phase.
Validation: The process of evaluating software at the end of software development to ensure compliance with intended usage.
[Introduction to Software Testing Paul Ammann, Jeff Offutt]
Also See:
Verification Methods
Verification & Validation Examples
Verification & Validation Questions