Eclipse is an integrated development environment (IDE) that makes extensive use of plugins for customization. The software is mostly written in Java, however, it may be used to develop a wide range of other programming languages.
Eclipse's code base was originally created based on IBM's VisualAge software. The software is released under the Eclipse Public License. It is currently maintained by the Eclipse Foundation.
Please note that questions that deal with the use of the IDE itself and other parts of the toolchain belong on Stack Overflow as described in the help center.