Bolero is an "American Style" Dance, which was introduced to United States in the mid-1930's. At that time, it was danced in its classical form, which was performed, to a constant beat of drums.
Originally a Spanish dance in 3/4 time, it was changed in Cuba initially into 2/4 time then eventually into 4/4. It is now danced as a very slow type of Rumba rhythm. The music is frequently arranged with Spanish vocals and a subtle percussion effect, played at a tempo of 20 to 25 mpm (measures per minute).
The Bolero is a modification of the Fandango, in which all the objectionable parts are omitted; but all the gracefulness is retained. It is has been said, that should the Bolero be played in the judicial halls or churches, the very judges and clergy could not refrain from joining in the general excitement of the dance.
This is a left turning dance based on a "slip pivot" (a slip pivot is a rotation of the body on the ball of the supporting foot creating a pivot either forward or backward). Bolero has body rise only (no foot rise). This coupled with the slip pivot and slow dreamy music gives Bolero a very slow, smooth, powerful, romantic look and feeling. The foot patterns are similar to Rumba but have a very different feeling.
The Bolero is often called the Cuban "Dance of Love", because of its slow and dreamy tempo, and it's beautiful melodies.
Although you may hear Rumba music which may seem slow enough to be a Bolero, the music is actually very different in tempo.