The Vietnamese word "ngủ lang" refers to the act of staying overnight at someone else's house without prior arrangement or invitation. It often implies sleeping over at a friend's or acquaintance's place in a casual or spontaneous manner, which can sometimes be seen as a bit inconsiderate if done too frequently.
While "ngủ lang" primarily refers to the act of sleeping over at someone else's place, the term can also carry a slightly negative connotation, suggesting a lack of consideration for the host's space or comfort.