Answer: Equal temperament
Explanation: This system divides the octave in 12 semitones related by the sequence Fₙ₊₁ = Fₙ*2^(1/12) (in frequency).
In the actual American notation, the 12 semitones are called:
A, A#, B, C, C#, D, D#, E, F, F#, G, G#.
This new intonation is very useful to avoid unpleasant harmonies, but none the less, it still sounds a little bit "off" when compared with just intonation (in the right key).
