What does "fen" mean?

Fen: Low land overflowed, or covered wholly or partially with water, but producing sedge, coarse grasses, or other aquatic plants; boggy land; moor; marsh. 'Mid reedy fens wide spread. Wordsworth. Note: Fen is used adjectively with the sense of belonging to, or of the nature of, a fen or fens. Fen boat, a boat of light draught used in marshes. -- Fen duck (Zoöl.), a wild duck inhabiting fens; the shoveler. [Prov. Eng.] -- Fen fowl (Zoöl.), any water fowl that frequent fens. -- Fen goose (Zoöl.), the graylag goose of Europe. [Prov. Eng.] -- Fen land, swamp land.