What is a separable affix?

Definition
	A separable affix is an affix that can be detached from its stem and located elsewhere in a construction.

Example (German)
	The affix an- is a separable affix. It is attached to its stem in the verb ankommen ‘to arrive’; but it can be detached from the stem, as in the sentence Ich komme an ‘I arrive’.

Generic
	A separable affix is a kind of
	What is an affix? (Linguistics)