A biplane is a fixed-wing aircraft with two main wings. The Wright brothers used a biplane design for the 1903 Wright Flyer I. Most aircraft in the early years of aviation were biplanes.
The biplane wing structure has a structural advantage but it produces more drag than a monoplane wing. It wasn't until the development of the a cantilever wing and aluminum alloys that monoplane wings became the norm.
Today biplanes are mostly used for aerobatics and agricultural aircraft.