An IDE is an Integrated Development Environment.

It’s a piece of software that provides the facility to develop other computer software easily; comprehensive IDE’s speed up the software development process by providing debugging tools and automation of the build process (translating high-level code into machine code), as well as many other features.
CLick Here for more info on IDE’s and software development - BBC Bitesize

Please Note: Links are up-to-date as of 07/19, but may not be maintained.