Intimate garments of people. Underpants, shorts, underpants. Plural interior. Internal part of a house, office or building. Furnished and accessories of offices or homes. They are inside, they are from the inside.
Areas or parts of a building or construction are not visible from the outside
1o_ Plural interior . 2o_ So, in the plural, it is a euphemism for underpants or underpants or any "underwear" that is not wanted or cannot be mentioned. See underpants.