Or is an instruction that takes an 8-bit input an compare sit with the accumulator. It checks to see if anything is set, and if neither are set, it results in a zero.
0 and 0 result: 0
0 and 1 result: 1
1 and 0 result: 1
1 and 1 result: 1
or a or b or c or d or e or h or l or ixh or ixl or iyh or iyl or (hl) or (ix+n) or (iy+n) or n ;8 bit constant
C and N flags cleared, P/V detects parity, and rest are modified by definition.
Used in bit-masking. For more information see here.
r denotes 8-bit register.