Friend

From CC Wiki

On the Casual Collective a friend is the name of people who were added via the friends system. This system allows users to see what they are doing, join their games, shout on their profile and send messages. A player can add a maximum of 100 friends, but can be added by others endlessly. Using the Gold Membership the amount of friends to be added is expanded to 150.

Mutual friends

Mutual friends are people that have been added by both users. Since the number of friends one can have is limited, but not the amount of times one can be added, for some users it is impossible to befriend everyone. There are several ways to figure out whether someone is a mutual friend, including whether or not blog comments can be made, or whether or not the user's position is visible on their profile's friends map.