Maris Otter is a two-row variety of barley, which was first introduced in 1966 in England. It was used by commercial breweries in the seventies, although its use declined in the eighties, culminating in its removal from the national list in 1989. Nowadays, it is used predominantly by home brewers and small breweries.
Beers with Maris Otter have a slightly nutty flavour, which has also been described as “biscuit flavour”. I like it for its added complexity of flavour over standard two-row pale ale malt, although it does not suit every beer.