According to http://dictionary.reference.com, a Business Suit is defined as “a suit, esp. one of conservative cut and color."

What makes up a man’s business suit?

            The first thing is the material used to make up the suit, such as the cloth and color. Normally, the suit has the same material used for the pants and jacket (and vest if used).  The color of the suit would be the same as well.  It can be a ready to wear, which means you can buy it at a department store, or tailor made, which means custom-made.  In England it’s, the “Bespoke” suit, which just means tailor made. The jacket can be either double-breasted (hehe) or single-breasted.