A blue-green deployment is a deployment strategy that involves running two separate environments, “blue” and “green,” with identical configurations. When deploying a new version, the new version is deployed to the inactive environment, and once tested and verified, traffic is switched to the new environment. 

Blue-green deployment is a release management technique that reduces risk and minimizes downtime. It uses two production environments, known as Blue and Green, to provide reliable testing, continuous no-outage upgrades, and instant rollbacks.