What is the bitwise OR operation?

In a nutshell

The bitwise OR operation takes two-bit patterns of equal length and performs the logical inclusive OR operation on each pair of corresponding bits.

The result in each position is 0 if both bits are 0. Otherwise, the result is 1.

   0101 (decimal 5)
OR 0011 (decimal 3)
 = 0111 (decimal 7)