Triband
A triband is a flag with three parallel bands. In strict flag usage it means three bands in only two colors, with the outer bands matching, as on the red, white and red flag of Austria. In looser usage it covers any three-band flag.
A three-band, three-color flag is called a tricolour, though many writers use the two words loosely. The bands do not have to be equal. Canada's flag has a white center twice as wide as each red side band, a variation sometimes called a Canadian pale.
The flag maker has horizontal and vertical band layouts. Set the outer bands to the same color for a triband, or change the middle one for a tricolour. A charge in the center band is a common addition. The flag design ideas guide has more examples.