Blue/Green Deployment
- New code deployed to second prod environment
- After testing, load balancer sends all prod traffic to new code
- Requires two production environments

Canary Testing
- New code deployed to second prod environment
- Small proportion of users directed to new code
- Requires two production environments

A/B Testing
- Run experiments of two different versions of a page in production
- Typically Javascript code changes the UI dynamically
- Does not require two production environments

Links:
Blue-green Deployments, A/B Testing, and Canary Releases
Blue Green Deployment, Canary Run, A/B testing difference