Also a form of male bonding to such a point where they start to seem like a couple.
This bond is normally only shared between two males that have a deeper understanding of each other, in a way no woman could ever realize.
Dating back to Plato and Socrates, a close but non-sexual relationship between two men. The whole is greater than the sum of the individual parts.
To girls this means, George Clooney + Brad Pitt>George Clooney or Brad Pitt