Definition of "fifties"

plural of fifty  examples

The decade of the 1850s, 1950s, etc.  examples

The decade of one's life from age 50 through age 59.  examples

(temperature, rates, plural only) The range between 50 and 59.  examples

From or evoking the 51st through 60th years of a century (chiefly the 1950s).  quotations  examples