C “power chord”. The so called power chord contains just the root (1) and 5th (5), here C (1) and G (5). Normally you will play a powerchord only with the low root on one of the two lowest strings and its 5th on the next string, but sometimes also with a second root an octave higher. Played with some overdrive/distortion, the power chord will give you a rock sound that is fat but not muddy.
Since a 3rd is completely missing, the powerchord is neither a minor nor a major chord and can consequently replace both kinds of chords. Sometimes even combinations/movements accross the boundaries of the key can sound interesting.