People who can count on each other for anything and everything. A friend is also able to be there for you no matter what, and true friends have a lot in common. They also like to talk shit about their roommates to each other knowing they won't say anything to the other. They may also drive the same car and have many other things in common by coincidence.
Megan: My birthday is April 23rd and my brother's is December 10th.
Friend Erin: OMG my birthday is April 26th and my brother's is December 7th! They're both 3 days apart! We were meant to be friends! :)