Continuous integration means running automated checks on every code change, usually through a service like GitHub Actions, GitLab CI, or CircleCI. For Drupal, typical checks include coding standards, PHPStan static analysis, PHPUnit tests, and security updates.
The pipeline triggers on every pull request, runs the checks, and blocks merging if anything fails. This catches problems before they reach main branches and keeps code quality consistent across the team.
Advanced pipelines also build the site in a container, run functional tests against it, and deploy to a staging environment automatically. GitLab CI and GitHub Actions both have strong support for these workflows. Setting up CI on a Drupal project takes time upfront but pays back quickly through fewer production issues and faster, more confident deployments. Every serious Drupal project should have at least basic CI in place.