CD can be defined as the processes and practices through which applications are made available to be deployed to production at any time.
Note
A key thing to note here is that the applications are made available for deployment to production but are not necessarily deployed. Having every build of your application deployed to production automatically is called continuous deployment. With Continuous Delivery, the builds may be deployed to a User Acceptance Testing (UAT) environment so that the different stakeholders can try out the application and then make a decision to deploy to production.
CD is a natural extension of CI. In other words, CI is the base on which a CD setup can be built, and it is not possible to even start talking about CD without thinking about CI. While CI enables integrating code written by different developers, CD is about ensuring that that the code is available for deployment to production in a timely and reliable manner.
CD, hence, involves...