A ridge formed on a plowed hillside.
Think of terraces on a hillside. Plowing across a hillside eventually forms terraces, as disturbed soil slides downhill to create a slight ridge - a positive lynchet - on the downhill side of the plowed area (a negative lynchet is created on the uphill side of the plowed area).
Etymology: diminutive form of Old English hlinc, ridge, rising ground.
Although traditionally associated with ancient fields in the British Isles, I learned the term from a book by Will Bonsall, who has created similar plowed terraces on his farm in Maine.