Requirements for calibration appear in most national and international quality standards, and most organizations recognize that measuring equipment must be calibrated. However, there is much confusion regarding the definition of calibration, and this confusion increases quality-related risks to organizations. The purpose of this technical bulletin is to sort out all the different concepts that exist for the term calibration, including official definitions and those in common use. The primary technical basis for this document is ASME B89.7.1-2016, Guidelines for Addressing Measurement Uncertainty, which is one of the few documents that has tried to sort out the calibration conundrum.