completely naked; in one's birthday suit
Euphemistic phrase literally meaning 'in the form as one was born'. Used to describe a state of total nudity.
He walked around the room completely naked.
When entering a hot spring, you become completely naked.
A set phrase composed of 生まれた (born), まま (as is), の (possessive particle), and 姿 (form, appearance). The literal meaning is 'the form as one was born', i.e., naked.