Idiom
The word Idiom has a couple of meanings in the APL world:
An expression recognized as such and understood without actually thinking about this. A typical example is nv/⍳⍴nv.
- An expression that is recognized by the interpreter and executed as a single operation; that should be faster than the APL operations it consists of.
- A single line of APL code designed to do something useful.
The last meaning is what we refer to as a phrase in the context of the PhraseBook project.
APL Wiki