CD is a philosophy around pushing your code to production: instead of giant, infrequent releases, it advocates many smaller changes, even multiple times per day. Today, most engineering teams are deploying at least once per day.
There's a lot required on the tooling end to make this a reality. One example is staging servers – they’re environments that mimic the actual app as closely as possible, so you can test reliably before sending the new build out to users.