When someone press the Like button on facebook, and you are going to check who liked someones comment, you assume who the liker is. The liker is usually the statuswriter or the poster of something, if someone gives a positive comment towards them.
Person A writes a status on facebook: Oh i just won 100 bucks on betting.
Person B writes on the status : Thats because you are so good at betting.
Then when someone likes Person B's and you dont know who it is, you check it, and right before you drag your mouse over the button, you assume it is Person A who likes it because the comment was ment positive towards that person.