CI/CD
Also known as: continuous integration, continuous delivery
CI/CD is the automated pipeline between a developer finishing a change and that change being live. Continuous integration is the first half: every change is merged frequently and automatically built, tested and checked. Continuous delivery is the second: anything that passes is packaged and can be deployed at the press of a button, or automatically.
Its real product is not speed but confidence. When every change is tested identically and deployed by the same script, releasing stops being an event that needs a quiet afternoon and becomes something that happens several times a day without ceremony.
It is also the cheapest quality control a project can buy. A test suite that runs on every change catches regressions while the author still remembers the code, which is a fundamentally different cost from finding it in production a month later.