What non K-Pop fans think:
Non-sexual relationship between two (or more) men.
In K-Pop context:
A cue for deafening fangirls screams of 'they must be dating!'.
K-Pop fans are generally very receptive to fan-service between idol groups' members and any form of bromance - hugs, holding hands and even standing side by side - would make the fans go into spazzing frenzy.