There are two basic types of suits: Single breasted and double breasted.
Single breasted suits come in two flavors: Two Piece Suits and Three Piece Suits. In the three piece version, the third piece is the waistcoat (or vest).
Three piece suits are not so popular these days because most offices and cars have air-conditioning and therefore do not require the protection of the third piece (waist coat).
For the same reason, the Bangladesh climate is particularly unsuitable for three-piece suits as they tend to be warmer. It is, however, not a bad idea to retain a three piece suit in the wardrobe for those particularly chilly winter days. I, however, don’t have any three piece suits.