Using hierarchical structurings in process design is a frequent process modeling technique. Subprocesses are a common way to enable hierarchical structuring. Current approaches have a tight view on the syntactical restrictions of subprocesses and do not investigate different autonomy properties in detail. This paper fills this gap and broadens the current subprocess definition to a spectrum of possibilities of subprocess notations. Thereby, three classifications are introduced: subprocess autonomy, interaction between parent process and subprocess, and execution of subprocesses.