Definitions of interchangeable:

• adjective:   (mathematics, logic) such that the arguments or roles can be interchanged

  Example: "The arguments of the symmetric relation, `is a sister of,' are interchangeable"

• adjective:   of or relating to or suggestive of complementation

  Example: "Interchangeable electric outlets"

• adjective:   capable of replacing or changing places with something else

  Example: "Interchangeable parts"