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.
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).
He has a wide range of hobbies, enjoying everything from music to sports.
This field has a narrow scope, but once you enter it, you can learn deeply.
This building has a wide frontage, and the shop entrance is large too.
This lot has a narrow frontage, so it's hard to build a shop on it.
The shop had a small frontage of three ken.
間口 is the width of a building or plot facing the street, while 奥行き is its depth from front to back.
Compound of 間 (ma, 'space') and 口 (kuchi, 'mouth/opening'), referring to the opening or frontage of a space. The reading まぐち is a straightforward combination of the kun'yomi readings.
The company expanded into a new field in order to broaden the scope of its business.