runner
The machine or container that runs a CI job's steps.
A runner is the host, provided by a CI service or self-hosted on the user's own machine, that checks out the code and executes a workflow's jobs.
Examples
When a pull request is opened, a fresh runner checks out the greenhouse node's repository and runs
./ci/run.shsteps from the workflow file.A runner is somebody's computer and somebody pays for its minutes, so check the CI provider's current billing before relying on free ones.