Continuous Integration is a software development methodology that expects developers to commit their code into a shared source code repository (e.g. git) several times a day as they work on new features or bug fixes. As soon as the code is checked-in, an automated build is kicked off that verifies the code works by running unit tests. If the unit tests pass, then there's some level of assurance that the changes did not break anything. The benefit of this methodology is that it allows teams to detect problems early.