A concept originating in Japan, whereas social interactions and dealings were considered more intimate and relaxed when they took place within a communal "onsen", or public bath.
This concept is still in some practice today, as when a business agent will meet a potential client for
dinner, or drinks, or on a racquetball court.
It has also evolved to define a situation of intimacy derived from the touch of
skin, or close proximity thereof, as in a
mother and child bonding from birth.
In Korea, as well as some other places, it has come to also
mean sexual contact, heavy petting, and related activities.