house lamb
/ˈhaʊs ˌlam/noun
1A lamb which, in order to ensure a tender meat, is reared in a building, typically fed on its mother's milk without being allowed out to graze, and slaughtered at between 6 and 10 weeks of age, traditionally in time for Christmas. Also: a lamb that is bottle-fed by a person and kept in or near their house; a pet lamb.
2The flesh of such a purpose-bred animal used as food.
Origin
Late 16th century; earliest use found in Edward Hellowes (fl. 1574–1601), courtier and translator. From house + lamb.