Undertone is the overall tone of your skin, most prominent when your face is bare. Your undertone can be either Cool, Neutral or Warm.
COOL - Skin has a pink or rosy undertone, sometimes sensitive, may burn easily when exposed to the sun.
NEUTRAL - Skin is neutral or balanced, not too pink, not too golden.
WARM - Skin has a golden or olive undertone, tans easily when exposed to the sun.
Use the Foundation Shade Finder to locate your skin's undertone and intensity, this will help you find the perfect shade suitable for you.
(C) Warm Undertone
(N) Cool Undertone