The Collaborative International Dictionary of English v.0.48:

iron-on \i"ron-on`\, a.
   Able to be attached (to clothing) by applying pressure and
   heat, as with a hand iron; -- of cloth items specially made
   with a glue that is softened by heat; -- used especially of
   patches to clothing or accessories to clothing, such as
   replacement pockets.
   [PJC]