How are Verification and Validation related with each other.

Verification and validation are independent procedures, that are used
together for ensuring that a product, service or a system meets requirements  and specifications and that it fulfils its intended objective.  

For complete testing of any application, both verification and validation need to
be performed and ignoring any one of them can introduce errors or can even  pass the products with bugs unidentified. This is the reason that most of the  SDLC models give importance to both Verification and Validation Processes.