In version 5 of the PMBOK guide, there was great attention paid to the difference between "Verification" and "validation." Verification was done by the project team and validation could only be done by the end-use.
At the time, this was to put the PMBOK's definitions more inline with other ANSI standards such as Systems Engineering.
Have things changed in version 6? The terms seem to be nearly interchangeable in Version 6. There's no clear distinction drawn between validation and verification Saving Changes...