While CI is usually easily understood, I feel that CD is often conflated with continuous deployment. Traditional CD is the process of building, testing and releasing software rapidly. Since testing is wrapped up in this definition, there is, of course, a natural relationship with CI. I view CD more on the spectrum of setting up automated systems so that the process of fixing a bug and deploying that fix safely and reliably to production is as fast and easy to hand off as possible.
Continuous deployment is a particular feature wrapped up within CD, that is, every merge to the production branch results in a deployment to the production system. A good CD pipeline enables continuous deployments, but it's up to the team behind the software ...
