testing – What is the current definition of continuous integration?

It seems that there are at least two possible definitions of continuous integration:

  1. Frequent merging of a codebase to a common codebase (e.g. daily merge to the main branch of a VCS server).
  2. Frequent building and testing of a codebase (e.g. build and test at each push to a VCS server).

Both 1 and 2 can be automated. 1 does not imply 2, and 2 does not imply 1.

What is the current definition of continuous integration? (Please back up your claim with a reference.)