Pas
[pah]
Step. A simple step or a compound movement which involves a transfer of weight. Example: pas de bourrée. "Pas" also refers to a dance executed by a soloist (pas seul), a duet (pas de deux). and so on.

Pas de quatre
[pah duh KA-truh]
A dance for four. The most famous pas de quatre in ballet history took place in London on July 12, 1845, at a command performance for Queen Victoria, when the four greatest ballerinas of the nineteenth century, Marie Taglioni, Carlotta Grisi, Fanny Cerrito and Lucile Grahn, appeared together.

Pas de trois
[pah duh trwah]
A dance for three. Similarly, a pas de cinq is a dance for five people; a pas de six is a dance for six people; etc.