Mutual friends on Facebook are friends the user has in common with someone else. This concept is also familiar to most people in offline life; a mutual friend is someone a person and another person are both friends with, whether these two people are familiar with each other or not.
If a Facebook user views a profile or hovers over a link to someone's profile, the names of several mutual friends with a link will be displayed in a small popup box if any exist. The mutual friends page will show all of the people that the user and the person whose profile is being viewed are both friends with on Facebook. This helps users determine if they know a certain person, and whether they are viewing the correct profile of a recent acquaintance who they wish to contact.
Users also have the option to suggest friends for others to add. If they wish to introduce their friends this way, they may click "..." at the top of a profile and click "Suggest Friends."
Mutual friends are often taken into consideration by Facebook for the "People You May Know" feature. This feature shows a user profiles of people they are likely to know offline. Other factors used in finding people the user may know include networks, workplaces, schools, locations and any imported address book information.