About
Continuous integration is just a fancy term for a build kicked off by a VCS commit.
Continuous Integration is the practice of testing each change done to your codebase automatically and as early as possible.
Not the same as Continuous Integration is a software development practice where members of a team integrate their work frequently, usually each person integrates at least daily - leading to multiple integrations per day.
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Software
See Code Shipping - Continuous (Deployment|Development|Delivery)
Environment variable
Continuous build will set the env CI=true to be able to recognize that the build script runs on a continuous server. For instance Travis