DevOps and Continuous Delivery enable Agile Development. They are complimentary. DevOps is a methodology and a set of practices where Continuous Delivery is an implementation that. (It’s more than that, but let’s use the above for this answer.) Continuous Delivery systems and processes push code out to production as often as the developers demand it. Some systems push code out several times per day like Etsy’s and others may be once per week or month.
Continuous Delivery is the means to enable Agile Development. Product managers write user stories (small feature requests) that get placed into the development pipeline. They are t-shirt sized, then worked on. At some point the developer will want to ship the code to various test environments and then out to production. Continuous Delivery systems facilitate the testing and moving code to different environments when the developer wants it to be shipped, which is usually when the user story is marked complete. (The previous is oversimplified). Without Continuous Delivery, developers would complete the user stories and there would be nothing to show until the next big release.