Lamb, hogget, and mutton, generically sheep meat, are the meat of domestic sheep, Ovis aries.
A sheep in its first year is a lamb and its meat is also lamb. A sheep in its second year and its meat are hogget. Older sheep meat is mutton. Generally, "hogget" and "sheep meat" are not used by consumers outside New Zealand and Australia, only the industry.
In South Asian, Australian, and Jamaican cuisine, "mutton" usually means goat meat.
Lamb is the most expensive of the three types and in recent decades sheep meat is increasingly only retailed as "lamb", sometimes stretching the accepted distinctions given above. The stronger-tasting mutton is now hard to find in many areas, despite the efforts of the Mutton Renaissance Campaign in the UK. In Australia, the term prime lamb is often used to refer to lambs raised for meat. Other languages, for example French, Spanish, Italian and Arabic, make similar or even more detailed, distinctions among sheep meats by age and sometimes by sex and diet, though these languages do not always use different words to refer to the animal and its meat — for example, lechazo in Spanish refers to meat from milk-fed (unweaned) lambs.
Classifications and nomenclature
The definitions for lamb, hogget and mutton vary considerably between countries. Younger lambs are smaller and more tender. Mutton is meat from a sheep over two years old, and has less tender flesh. In general, the darker the colour, the older the animal. Baby lamb meat will be pale pink, while regular lamb is pinkish-red.
- Lamb — a young sheep under 12 months of age which does not have any permanent incisor teeth in wear. (From July 1, 2019, the Australian definition is "an ovine animal that: (a) is under 12 months of age; or (b) does not have any permanent incisor teeth in wear."  The New Zealand definition also allows "0 incisors in wear".)
- Hogget — A term for a sheep of either sex having no more than two permanent incisors in wear, or its meat. Still common in farming usage, it is now rare as a domestic or retail term for the meat. Much of the "lamb" sold in the UK is "hogget" to a farmer in Australia or New Zealand.
- Mutton — the meat of a female (ewe) or castrated male (wether) sheep having more than two permanent incisors in wear.
The term "hogget" is uncommon in the United States. Federal statutes and regulations dealing with food labeling in the United States permit all sheep products to be marketed as "lamb." Sheep products less than 12–14 months old can be labeled "prime lamb" or "choice lamb" and all other sheep meat can be labeled simply as "lamb."
The term "mutton" is applied to goat meat in most of these countries, and the goat population has been rising. For example, mutton-curry is always made from goat meat. It is estimated that over one-third of the goat population is slaughtered every year and sold as mutton. The husbanded sheep population in India and the Indian subcontinent has been in decline for over 40 years and has survived at marginal levels in mountainous regions, based on wild-sheep breeds, and mainly for wool production.
- Milk-fed lamb — meat from an unweaned lamb, typically 4–6 weeks old and weighing 5.5–8 kg; this is almost unavailable in countries such as the United States and the United Kingdom. The flavour and texture of milk-fed lamb when grilled (such as the tiny lamb chops known as chuletillas in Spain) or roasted (lechazo asado or cordero lechal asado) is generally thought to be finer than that of older lamb, and fetches higher prices. The areas in northern Spain where this can be found include Asturias, Cantabria, Castile and León, and . Milk-fed lambs are especially prized for Easter in Greece, when they are roasted on a spit.
- Young lamb — a milk-fed lamb between six and eight weeks old
- Spring lamb — a milk-fed lamb, usually three to five months old, born in late winter or early spring and sold usually before 1 July (in the northern hemisphere).
- Sucker lambs — a term used in Australia — includes young milk-fed lambs, as well as slightly older lambs up to about seven months of age which are also still dependent on their mothers for milk. Carcases from these lambs usually weigh between 14 and 30 kg. Older weaned lambs which have not yet matured to become mutton are known as old-season lambs.
- Yearling lamb — a young sheep between 12 and 24 months old, so another term for a hogget.
- Saltbush mutton – a term used in Australia for the meat of mature Merinos which have been allowed to graze on atriplex plants
- Salt marsh lamb (also known as 'saltmarsh lamb' or by its French name, agneau de pré-salé) is the meat of sheep which graze on salt marsh in coastal estuaries that are washed by the tides and support a range of salt-tolerant grasses and herbs, such as samphire, sparta grass, sorrel and sea lavender. Depending on where the salt marsh is located, the nature of the plants may be subtly different. Salt marsh lamb has long been appreciated in France and is growing in popularity in the United Kingdom. Places where salt marsh lamb are reared in the UK include Harlech and the Gower Peninsula in Wales, the Somerset Levels, Morecambe Bay and the Solway Firth.
- Saltgrass lamb – a type of lamb exclusive to Flinders Island (Tasmania). The pastures on the island have a relatively high salt content, leading to a flavor and texture similar to saltmarsh lamb.