Elementary instruction designed to develop the sense of hearing as applied to music (for example: recognition of pitch, of intervals, chords, meter, rhythmic patterns, etc.)
Musicians learn to identify pitches, intervals, melodies, chords, rhythms, etc by hearing.
Sometimes referred to as Solfeggio, which is the general instruction in all fundamentals of music.
Applying it to your online piano lessons
When learning how to play the piano, it is essential to have a great ear. The only way to get better is to practice ear training as discussed today. Not only will it give you a better ear for chords and melodies but also give you a better feel in general, especially when you play with other musicians.
I cannot stress enough how much this will benefit you as a piano player. It may be a bit difficult at first, but keep at it and I promise it will get easier and you will see the rewards in no time.