What are high fidelity headphones?

The main performance of IEC 581-10 high fidelity earphone is as follows:

The frequency response is not less than 50 Hz to 12500 Hz, and the allowable error of typical frequency response is ± 3 dB;

The difference between the frequency response curves of two earphones for dual channel (such as stereo) corresponding to the average sound pressure level of each octave (with the center frequency in the range of 250 ~ 8000Hz) shall not be greater than 2dB;

In the range of 100hz-5000hz, when the sound pressure level is 94db (based on 20upa), the harmonic distortion does not exceed 1%, and does not exceed 3% at 100dB