Teff, tef, or t'ef is a grain which is also known by the pleasing name lovegrass and the less poetic annual bunch grass; it is thought to have been domesticated in North Africa in prehistoric times. Now grown in small quantities in various parts of the world for food and animal fodder, teff remains a staple in North Africa. You're most likely to have eaten it in the spongy sourdough bread injera, which is often made from teff flour. Teff is a hardy plant that grows well in conditions ranging from water logged to drought-dry, but because it is labour intensive to harvest, it is expensive to buy in its native lands. Thus poorer people must make their injera from other grains, though they are said to produce a bitter bread. Injera made from teff is considered to be the most delicious.
The word teff may derive from the Amharic word teffa, "lost," perhaps because of the small size of the grain and how easy it is to lose if dropped. It is the smallest commonly eaten grain in the world: each seed is only about 1/32 of an inch in diameter and it takes about 150 grains of teff to equal the volume of one grain of wheat. Because of its small size, the bulk of teff is made up of nutritious bran and germ, parts of grain that are often removed when milling larger grains; teff is too small to be milled. Teff is thus rich in protein and fibre. Teff is also high in iron, which is why there is little anemia in North Africa, and it's higher in calcium than other grains: one cup of cooked teff contains more calcium than a cup of milk. It contains no gluten - which is why injera is so flat - and has a good amino acid balance, being particularly rich in lysine.
The tiny grains can be pale ivory, deep brown, or even purple, depending on the variety. The lightest coloured teff is the most difficult to grow, and just as white bread has been a status symbol in the west and white rice in the east, so it is in Ethiopia: only the richest and most prestigious families could afford to consume "white" teff. Poorer families are left to eat the darker varieties, while cattle consume the hay. Teff is mild flavoured with a slight nutty flavour. The seeds can be a bit mucilaginous, which makes them clump together when cooked; for this reason they make a good thickener for soups and stews. It can be mixed with other grains or ground into flour, and lots of people have adapted baked goods recipes to include teff in this form.