Thundercracker was silent for a moment, absorbing all of that.  When he spoke again, it was quietly, his gaze on the floor somewhere in front of him.  "It…it means…I don't know what equivalent you might recognize.  As far as I know, symbiotes like Soundwave and his cassettes are probably the closest, at least in my reality.  I've heard it equated to family or brothers, though I'm not sure that's quite right either.  But it means having a special, deep bond with someone.  Usually two others, though it can be more, sometimes up to five or six, though anything other than three is fairly rare."