noun
frontage; width of a building or plot
Refers to the width of the front of a building or a plot of land facing a road. Often used in real estate contexts.
この土地は間口が狭いが、奥行きは十分にある。
This plot has a narrow frontage, but it is deep enough.
Figurative extension of the physical width meaning, used to describe the breadth of one's knowledge, experience, or the scope of one's work. Often appears in phrases like 間口が広い (broad) or 間口が狭い (narrow).
彼は趣味の間口が広く、音楽からスポーツまで何でも楽しむ。
He has a wide range of hobbies, enjoying everything from music to sports.
この仕事は間口が狭いが、一度入れば深く学べる。
This field has a narrow scope, but once you enter it, you can learn deeply.