Final answer:
A woodwind quintet is unique because it includes a brass instrument, the horn, which complements the traditional woodwind instruments.
Step-by-step explanation:
A woodwind quintet is unusual in that it includes a brass instrument. Typically, a woodwind quintet consists of five instruments: flute, oboe, clarinet, bassoon, and horn. The horn, despite being a brass instrument, is traditionally included due to its ability to blend well with the woodwinds, rounding out the quintet's sound with its rich harmonics.