What is Ditch?

Legal Definition
A ditch is a small to moderate depression created to channel water. A ditch can be used for drainage, to drain water from low-lying areas, alongside roadways or fields, or to channel water from a more distant source for plant irrigation. A trench is a long narrow ditch. Ditches are commonly seen around farmland, especially in areas that have required drainage, such as The Fens in eastern England and much of the Netherlands.

Roadside ditches may provide a hazard to motorists and cyclists, whose vehicles may crash into them and get damaged, flipped over or stuck, especially in poor weather conditions, and in rural areas.

In Anglo-Saxon, the word dïc already existed and was pronounced "deek" in northern England and "deetch" in the south. The origins of the word lie in digging a trench and forming the upcast soil into a bank alongside it. This practice has meant that the name dïc was given to either the excavation or the bank, and evolved to both the words "dike"/"dyke" and "ditch". Thus Offa's Dyke is a combined structure and Car Dyke is a trench, though it once had raised banks as well. In the midlands and north of England, a dike is what a ditch is in the south, a property boundary marker or small drainage channel. Where it carries a stream, it may be called a running dike as in Rippingale Running Dike, which leads water from the catchwater drain, Car Dyke, to the South Forty Foot Drain in Lincolnshire (TF1427). The Weir Dike is a soak dike in Bourne North Fen, near Twenty and alongside the River Glen.
-- Wikipedia
Legal Definition
The words "ditch" and "drain" have no technical or exact meaning. They both may mean a hollow space in the ground, natural or artificial, where water is collected or passes off. Goldthwait v. East Bridgewater, 5 Gray (Mass.) 64; Wetmore v. Flake, 15 In I. 354, 5 All. 375.
-- Black's Law Dictionary