A project can have one or several upstream projects, which means that current project is scheduled depending if the upstream project is built successfully or not. If the upstream project is successful, then the current project is added to the build queue. If the upstream project is broken, then the current project will not be added to the build queue.
Downstream project
A project can have one or several downstream projcets. The downstream projects are added to the build queue if the current project is built successfully. It is possible to setup that it should add the downstream project to the call queue even if the current project is unstable (default is off).
Stable build
A build is stable when it was built successfully and no publisher is reporting it as unstable.
Unstable build
A build is unstable when it was built successfully and one or several publishers has reported it as unstable. For example if the JUnit publisher is configured and a test fails then the build will go from stable to unstable.
Broken build
A build is broken when it failed during building it.
Slave
Slaves are computers that are set up to build projects for a master. Hudson runs a separate program called "slave agent" on slaves. When slaves are registered to a master, a master starts distributing loads to slaves.
Terminology