noun
U-shaped gutter; U-ditch
A concrete drainage channel with a U-shaped cross-section, commonly used in road and construction contexts.
道路の脇にＵ字溝が設置されている。
U-shaped gutters are installed along the side of the road.
工事現場でＵ字溝を並べて排水路を作る。
At the construction site, they line up U-ditches to make a drainage channel.
側溝 is a general term for roadside gutters, while Ｕ字溝 specifically refers to the U-shaped concrete type.
Compound of the Latin letter U (for the shape), 字 (character), and 溝 (gutter, ditch).