It's a knitted garment like a sweater or cardigan but in a heavy weight and shaped like a coat. So typically longer, warmer, more structured than a cardigan. Designed for outdoor/outer wear. With large coat buttons or a wrap and tie closure. Lisa's has toggles like a duffle coat.
Or to approach from the other direction, a coat made out of a heavy, chunky knit rather than woven or felted material.