Usually but not always referring to the bond that forms between two males. Similar in principle to the relationship between to brothers in that the two men in question can always rely on each other even when times are tough. Sometimes clingy girlfriends get offended at the concept of "male comraderie".
Guy: Baby I just miss that sense of comraderie that I had with my friends.
Girl: But don't you feel it with me honey?
Guy: You're my girlfriend, it's not the same thing.