Fifties meaning : The decade of the 1850s, 1950s, etc. The decade of one's life from age 50 through age 59. (temperature, rates) The range between 50 and 59. From or evoking the 51st through 60th years of a century (chiefly the 1950s). A banknote or coin with a denomination of 50. A batsman's score of at least 50 runs and less than 100 runs.