CI is the process of shortening the integration cycles. Whereas in traditional software, many different features could have been developed separately and only integrated prior to release, in projects developed with CI, integration can occur several times a day. Usually, each change a developer makes is tested and integrated at the same time as it is committed to the central repository.
Since testing occurs just after development, the feedback loop is much quicker. This lets developers fix bugs more easily (as they usually still remember what was changed). In contrast to the traditional approach of testing just prior to release, CI saves a lot of work and improves the quality of software.
