This document provides a unified collection of the commonly used terms and definitions in the area of LED thermal measurements. The terms and definitions provided herein extend beyond those used in the JESD51 family of documents, especially in JESD51-13, in order to include other often used terms and definitions in the area of light output measurements of LEDs. Definitions, symbols and notations regarding light output measurements used here are consistent with those defined in JESD77C.01 and with those defined by CIE (International Commission on Illumination), especially in the International Lighting Vocubulary, CIE S 017/E:2011 ILV and in the CIE 127-2007 document as well as in some other relevant standards of other standardization bodies from the solid-state lighting industry, e.g., ANSI/IESNA RP 16- 05.