1. An acronym for either Intelligent Drive Electronics or Integrated Drive Electronics, based on which manufacturer's data sheet you peruse. An IDE interface is an interface for mass storage devices, in which the controller is integrated into the disk or CD-ROM drive. The technology evolved from the late 1980s and is greatly advanced in capability over the original specifications. The popularity was mainly due to the universal acceptance of the idea and the low cost of manufacturing. Although it really refers to a general technology, most people use the term to refer the ATA specification, which uses this technology. See ATA.
2. An acronym for Integrated Development Environment. A method of writing software using varied languages and styles, into one end application. An example of a simplified IDE is HTML and scripting. PHP is heavily moving to IDE as a normal environment.