In Forth, it is customary to explain a word's action by drawing the top of the stack before and after the word's execution. The two halves are separated by `--'. For instance,

/MOD ( n_{1} n_{2} -- mod quot)

means that

/MOD takes

2 numbers and returns `mod' (presumably

`n`_{1} MOD n_{2}

, although the stack diagram only implies it if you know some

conventions) and `quot' (presumably

`n`_{1} DIV n_{2}

).

The space after the open-parentheses is important: it makes the entire stack diagram a legal Forth comment. Stack diagrams are often written in just this format at the definition of the word:

: ABS ( n -- u)
dup < if negate then ;