In summary, FWIW, from Marc's second link:
verification - conformation by examination and provision of objective evidence that specified requirements have been fulfilled. (ISO Standard 8402)
validation - confirmation by examination and provision of objective evidence that the particular requirements for a specific intended use are fulfilled. (ISO Standard 8402)
calibration - a set of operations that establish, under specified conditions, the relationship between values of quantities indicated by a measuring instrument or measuring system or values represented by a material measure or a reference material, and the corresponding values realized by the standard.
NOTES
1 The result of a calibration permits either the assignment of values or measurands to the indications or the determination of corrections with respect to indications.
2 A calibration may also determine other metrological properties such as the effect of influence quantities.
3 The result of a calibration may be recorded in a document sometimes called a calibration certificate or a calibration report. (International Vocabulary of Basic and General Terms in Metrology)
Sounds like some of the terms sometimes overlap.
I hope there is not a test on this tomorrow!