In the context of using PowerShell commands with managed code a runspace is the operating environment for the commands invoked by the host application.
This environment includes the commands and data that are currently present, and any language restrictions that currently apply.Host applications can use the default runspace that is provided by Windows PowerShell, or they can create their own runspaces by using the RunspaceFactory class. By using that class, The host application can create individual runspaces or they can create a pool of runspaces. Once a runspace is created and opened, the host application can invoke commands synchronously or asynchronously by using a PowerShell object. For more information see Writing a Windows PowerShell Host Application