Final answer:
The logic instruction used to know when one or both matching bits are on in two different words is the bitwise OR operator.
Step-by-step explanation:
The logic instruction that is used to know when one or both matching bits in two different words are on is called the bitwise OR operator. It is commonly represented as the symbol | (pipe). This operator compares each bit of the two words and returns 1 if at least one of the bits is 1.
For example, if we have two words: 1010 and 1100, the bitwise OR operation would result in 1110. This means that the second and fourth bits are matching and turned on.