The party with a majority of seats is known as the majority party; if two or more parties in opposition are tied, the Vice President's affiliation determines which party is the majority party. The next-largest party is known as the minority party. The President pro tempore, committee chairmen, and some other officials are generally from the majority party; they have counterparts (for instance, the "ranking members" of committees) in the minority party. Independents and members of third parties (so long as they do not caucus with or support either of the more numerous parties) are not considered in determining which is the majority party.
http://en.wikipedia.org/wiki/United_States_SenateThe current situation is a bit interesting; at this point I'm not sure who the majority party will be.
Even if both MT and VA are won by the Dems, there may be a struggle for each party to be considered the acting majority. It might all come down to what Lieberman does ...
- Make7