sing-along

[sing-uh-lawng, -long] /ˈsɪŋ əˌlɔŋ, -ˌlɒŋ/
noun
1.
an informal or unrehearsed singing of songs by a group of people, usually under the direction of a leader; songfest.
2.
an occasion marked by such singing.
Also, singalong.
Origin
1955-60; noun use of verb phrase sing along
British Dictionary definitions for sing along

sing along

verb (intransitive, adverb)
1.
to join in singing with a performer
noun
2.
such a singsong
Word Origin and History for sing along

sing-along

1959, noun and adjective, from verbal phrase; see sing (v.) + along (adv.). Originally associated with U.S. music producer Mitch Miller (1911-2010).