Continuous Delivery - aka CD - builds on Continuous Integration, in that it automates the deployment process of the previously created builds.
Usually, all releases to non-production environments are triggered also automatically, whereas the release to production always requires a manual approval (think: ack-button). Key is that Automated Releases are leveraged - there are no manual components.
The difference to Continuous Deployment is that triggering of releases to environments is optional and triggering of release to production always requires human supervision.
- Wikipedia: Continuous delivery
- Atlassian: Continuous integration vs. continuous delivery vs. continuous deployment