Wikipedia
A French drain or weeping tile (also blind drain, rubble drain, rock drain, drain tile, perimeter drain, land drain, French ditch, sub-surface drain, sub-soil drain or agricultural drain) is a trench filled with gravel or rock or containing a perforated pipe that redirects surface water and groundwater away from an area. A French drain can have perforated hollow pipes along the bottom (see images) to quickly vent water that seeps down through the upper gravel or rock.
French drains are primarily used to prevent ground and surface water from penetrating or damaging building foundations. Alternatively, French drains may be used to distribute water, such as a septic drain field at the outlet of a typical septic tank sewage treatment system. French drains are also used behind retaining walls to relieve ground water pressure.
Usage examples of "french drain".
Cadmann had finished digging the French drain--the rock-filled slit, a foot wide, five feet long and three deep, at the uphill mouth of their home.
When I found frogs coming up out of the ancient French drain, it was amusing.