CI/CD stands for Continuous Integration and Continuous Deployment. Continuous Integration means code changes are automatically tested as soon as they're committed. You push code, the CI system checks it out, runs tests, lints it, builds it. If anything fails, you know immediately. Bugs are caught before reaching production.
Continuous Deployment means passing builds are automatically deployed to production. No manual deployment step. No release process. Code is automatically promoted from development to production when it passes tests. Fast iteration becomes possible. You can push code and have it live in production within minutes.
Rapid experimentation is practical because rollback is as simple as redeploying the previous version. The risk is that bad code reaches production, but good test coverage mitigates this. CI/CD is table stakes for professional software development. GitHub Actions, GitLab CI, Jenkins, CircleCI, Travis CI, there are many platforms. The concept is identical.
Automation catches problems early and gets code to users fast.