Istilah

ISTILAH اصلاح
Pl. Istilahat. A phrase; a term; idiom. A theological term.
The author of the Kitabu ‘t-Ta’rifat says it is the agreement of a tribe, or sect, or party, to give a special meaning to a word, ever and above that which it has in its literal sense, but which is in accordance with it.

Based on Hughes, Dictionary of Islam