An inadvertent mistake by a software developer that sometimes stops the build process, or causes unacceptable warnings, and/ or failures in the automated test environments, is known as a "Build Breaker". The onus on the developer then, is to get the build to normal as soon as possible.
Continuous integration is a key attribute of products developed via agile methodology. But as is the human nature, developers may sometimes make mistakes and inadvertently commit bugs to the software repository. When such a commit stops the build/compile process or causes unacceptable warnings or failures in the automated test environment or a combination of these, the build is said to be broken. The developer is said to have committed a build breaker. It is generally a priority to get the build to normal as soon as possible and the responsibility for this lies with the developer involved.