the 50th anniversary of a significant event
late 14c., in the Old Testament sense, from Old French jubileu "jubille; anniversary; rejoicing," from Late Latin jubilaeus "the jubilee year," originally an adjective, "of the jubilee," altered (by association with Latin jubilare "to shout with joy") from Greek iabelaios, from iobelos, from Hebrew yobhel "jubilee," formerly "a trumpet, ram's horn," literally "ram."
The original notion was of a year of emancipation of slaves and restoration of lands, to be celebrated every 50th year (Levit. xxv:9); it was proclaimed by the sounding of a ram's horn on the Day of Atonement. The Catholic Church sense of "a period for remission of sin penalties in exchange for pilgrimages, alms, etc." was begun in 1300 by Boniface VIII. The general sense of "season of rejoicing" is first recorded mid-15c., though through early 20c. the word kept its specific association with 50th anniversaries. As a type of African-American folk song, it is attested from 1872.
a joyful shout or clangour of trumpets, the name of the great semi-centennial festival of the Hebrews. It lasted for a year. During this year the land was to be fallow, and the Israelites were only permitted to gather the spontaneous produce of the fields (Lev. 25:11, 12). All landed property during that year reverted to its original owner (13-34; 27:16-24), and all who were slaves were set free (25:39-54), and all debts were remitted. The return of the jubilee year was proclaimed by a blast of trumpets which sounded throughout the land. There is no record in Scripture of the actual observance of this festival, but there are numerous allusions (Isa. 5:7, 8, 9, 10; 61:1, 2; Ezek. 7:12, 13; Neh. 5:1-19; 2 Chr. 36:21) which place it beyond a doubt that it was observed. The advantages of this institution were manifold. "1. It would prevent the accumulation of land on the part of a few to the detriment of the community at large. 2. It would render it impossible for any one to be born to absolute poverty, since every one had his hereditary land. 3. It would preclude those inequalities which are produced by extremes of riches and poverty, and which make one man domineer over another. 4. It would utterly do away with slavery. 5. It would afford a fresh opportunity to those who were reduced by adverse circumstances to begin again their career of industry in the patrimony which they had temporarily forfeited. 6. It would periodically rectify the disorders which crept into the state in the course of time, preclude the division of the people into nobles and plebeians, and preserve the theocracy inviolate."