A canary launch allows you to gradually release new features to a subset of your users while still serving your current branch to the rest of your users. It basically allows you to test things in parallel without having to make major merges/deployments. This allows you to A/B test features to assess performance before releasing them to a majority of your users.
A canary launch (aka canary deployment or canary release) is rolling features out to a small number of users to assess the reaction of the overall system. Are users happier? Is more money made? Does the new feature increase system load? A canary launch allows you to roll out a feature slowly, and measure the reaction from real user “canaries”, looking for early indicators of danger. If a feature is not good, it can rolled back. Canary launches are a best practice for agile development organizations practicing continuous delivery to move faster.