1.
kitchen door; back entrance; service entrance
A secondary entrance to a house, typically located near the kitchen. Used for everyday comings and goings, deliveries, and taking out trash, as opposed to the formal front entrance.
A compound of 勝手 (kitchen; one's own convenience) and 口 (entrance). In traditional Japanese homes, 勝手 referred to the kitchen area, so the 勝手口 was the door leading to or near the kitchen — a secondary, informal entrance.
Cultural note
In Japanese houses, the 玄関 (front entrance) is for formal use and welcoming guests, while the 勝手口 is for practical daily use: taking out garbage, receiving deliveries, and stepping into the garden. Many modern apartments lack a 勝手口, but houses commonly have one.