Modulus

x mod y    mod[x;y]

Where x and y are numeric, returns the remainder of x%y.

q)-3 -2 -1 0 1 2 3 4 mod 3
0 1 2 0 1 2 0 1

q)7 mod 2 3 4
1 1 3

q)-7 7 mod/:\:-2.5 -2 2 2.5
-2   -1 1 0.5
-0.5 -1 1 2