1. A low tract of land, especially one that is moist or marshy, often with ranker vegetation than that of the adjacent higher lands.
2. A valleylike intersection of two slopes in a piece of land.
3.A manmade ditch designed to manage water runoff, filter pollutants, and increase rainwater infiltration.
Origin: 1400-50; late Middle English; originally a cool, shady spot, perhaps Old Norse svalr meaning cool, or svalir meaning a covered porch.