"Continuous delivery (CD) is a software engineering approach in which teams produce software in short cycles, ensuring that the software can be reliably released at any time."
"In software engineering, continuous integration (CI) is the practice of merging all developer working copies to a shared mainline several times a day."
"Continuous deployment means that every change is automatically deployed to production. Continuous delivery means that the team ensures every change can be deployed to production but may choose not to do it, usually due to business reasons. In order to do continuous deployment one must be doing continuous delivery."
Continuous integration < continuous delivery < continuous deployment (sort of).