Pipeline
A pipeline describes the ordered path an artefact takes to production. It lives in your repository and is versioned with the code it deploys.
Environment
An environment is a named target with its own configuration. Environments form a chain and inherit from one another, so shared values are declared once.
Promotion
A promotion moves an existing artefact from one environment to the next. It never rebuilds. The artefact identifier is identical on both sides.
Policy
A policy states what must be true before a promotion is allowed — required checks, number of approvals, and who may give them.