A yearling is a young animal that has passed its first birthday but is not yet two years old — so somewhere between one and two. The word is used most of all for horses, and that is where you meet it in real life: a yearling sale is an auction of one-year-old horses that people buy hoping they will grow into fast racehorses. Big money and big hopes sit on those animals, which is why racing news is full of the word. It is also used for young cattle, sheep, deer, and some fish. Farmers and racing people use it in a very exact way, because an animal's age changes what it can do and what it is worth; ordinary speakers hardly use it at all. Note that a yearling is old enough to be away from its mother but too young to work or race hard — it is roughly the animal version of a teenager. One useful detail for horses: in the racing world every horse counts its birthday from the 1st of January, so a foal born in May becomes a 'yearling' the following January, not on the day it actually turns one. The word can also come before a noun — 'a yearling colt', 'yearling sales'.