Continuous delivery (CD) is an extension of the concept of continuous integration (CI). Whereas CI deals with the build/test part of the development cycle for each version, CD focuses on what happens with a committed change after that point. With continuous delivery, any commit that passes the automated tests can be considered a valid candidate for release.
An important goal of continuous delivery is to make feedback loops as short as possible. Because code is delivered in a steady stream to user acceptance testing (UAT) or the staging environment, cause and effect can be observed early and code can be tested for all aspects of functionality, including business rule logic (something unit tests can't do reliably).
If an iterative process is becoming unwieldy due to increasing project complexity, CD offers developers a way to get back to doing smaller, more frequent releases that are more reliable, predictable and manageable. When CD is ongoing and testing occurs early, a concept sometimes referred to as "shift left," developers can start working on fixes before they have moved on to another aspect of the development project. This can help increase productivity because it minimizes the effort that's required for developers to refocus on the initial task.