The core to PowerShell is the runtime, the execution engine that implements command processing. It includes the classes that provide the interface between the hosting application and PowerShell commands and providers. The PowerShell runtime is implemented as a runspace object for the current PowerShell session, which is the operational environment in which the shell and the commands execute.
A runspace provides a way for a hosting application to execute pipelines programmatically. Runspaces construct a logical model of execution using pipelines that contains Cmdlets, native commands, and language elements.