A lynchet is a bank of earth that builds up on the downslope of a field ploughed for a long period of time. The disturbed soil slips down the hillside to create a positive lynchet whilst the area reduced in level becomes a negative lynchet. They are also referred to as strip lynchets.
They are a feature of ancient field systems such as the Celtic fields of the British Isles. Some opinions believe that they were passively formed under the long-term action of gravity and weathering on the loosened soil of a ploughed slope, while others believe they may have been intentionally formed, to prevent erosion and slippage of the ploughed slope. (from Wikipedia)