A more thorough explanation:

Definition: Earmark is a noun that originally referred to a mark made on the ear of animals like sheep to identify them.

Example: In the past, farmers would use an earmark to distinguish their sheep from those of other farmers. They would make a small cut or notch on the ear of each sheep to indicate ownership.

Explanation: The example illustrates how earmark was used to identify animals. Farmers would use earmarks to distinguish their own animals from those of other farmers. This helped them keep track of their livestock and prevent theft.