The movement of any service component or other configuration item into any environment (e.g., test, staging, production). Deployment is distinct from "Release" (which makes a feature available to users); deployment is the technical act of moving the bits.
Decoupling deployment from release allows for techniques like "Dark Launches" and "Canary Deployments," reducing the risk of software updates.
Deployment should be a non-event. It should happen hundreds of times a day, handled entirely by robots. If your deployment requires a "Go/No-Go" meeting and a pizza party for the team staying late, you are doing it wrong. We automate deployment so humans can focus on Release (measuring value).