A CI/CD pipeline (Continuous Integration and Continuous Deployment) is an automated workflow that takes code changes from a developer's machine, runs a series of checks against them, and pushes the changes to a server when those checks pass. Continuous Integration is the merging-and-testing half — every time someone commits, the pipeline runs the test suite, linters, and security scans against the merged code. Continuous Deployment is the shipping half — when CI passes on the main branch, the pipeline pushes the result to a staging or production server without a human pressing a button.
I use CI/CD on every WordPress site I run that's complex enough to have more than one author. Even on smaller sites, the pipeline catches a useful number of issues before they reach a server: a missed PHP syntax error, a CSS file that didn't compile, a plugin update that broke a custom hook.
The usual stack on WordPress projects is GitHub Actions or GitLab CI for the runner, with steps that run PHPCS for coding standards, PHPStan for static analysis, a build step for compiled assets, and a deploy step that pushes to the host. WP Engine, Pantheon, and Kinsta all support git-push deploys, which makes the deploy step a one-line command.
The payoff isn't speed — it's predictability. With a pipeline, every release follows the same path. Without one, every release is a slightly different sequence of FTP uploads, plugin updates, and "did anyone test this?" Slack messages. The first kind is recoverable; the second eventually breaks something visible.