Overview
Easy rider is an archaic United States slang expression whose meaning has varied with time.
History
Origins
Easy rider originally meant an expert horseman or a horse that was easy to ride.
1900s
In the early 1900s the term took on the meaning of freeloader as found in the old song "We Don't Care What Mr. Crump Don't Allow", based on "We Don't Care What Mama Don't Allow":
Mr. Crump won't 'low no easy riders here,
Mr. Crump won't 'low no easy riders here,
We don't care what Mr. Crump don't 'low,
We goin' to bar'l-house anyhow—
Mr. Crump can go and catch hisself some air!
From Wikipedia (CC BY-SA 4.0).