Originally, in the days before automobiles, jingle bells were strapped to a horse's harness as a way to avoid collisions at blind intersections, as a horse-drawn sleigh makes very little noise as it glides over the snow.
The history of the song "Jingle Bells" is somewhat more provocative. According to Wikipedia:
"Jingle Bells was often used as a drinking song at parties: people would jingle the ice in their glasses as they sung. The double-meaning of "upsot" was thought humorous, and a sleigh ride gave an unescorted couple a rare chance to be together, unchaperoned, in distant woods or fields, with all the opportunities that afforded. Sleigh rides were the nineteenth-century equivalent of taking a girl to a drive-in movie theatre in the 1950's and early 1960's, so there was a somewhat suggestive and scintillating aspect to the song that is often now unrecognized."
Here are the full lyrics to the song:
Jingle Bells
Dashing through the snow
In a one-horse open sleigh
O'er the fields we go
Laughing all the way
Bells on bobtail ring
Making spirits bright
What fun it is to ride and sing
A sleighing song tonight!
Jingle bells, jingle bells,
Jingle all the way.
Oh! what fun it is to ride
In a one-horse open sleigh.
Jingle bells, jingle bells,
Jingle all the way;
Oh! what fun it is to ride
In a one-horse open sleigh.
A day or two ago
I thought I'd take a ride
And soon, Miss Fanny Bright
Was seated by my side,
The horse was lean and lank
Misfortune seemed his lot
He got into a drifted bank
And then we got upsot.
|: chorus :|
A day or two ago,
The story I must tell
I went out on the snow,
And on my back I fell;
A gent was riding by
In a one-horse open sleigh,
He laughed as there I sprawling lie,
But quickly drove away.
|: chorus :|
Now the ground is white
Go it while you're young,
Take the girls tonight
and sing this sleighing song;
Just get a bobtailed bay
Two forty as his speed
Hitch him to an open sleigh
And crack! you'll take the lead.