C major refers to a natural major key in music that starts with the C note. C major is a relatively stable and moderate white key, as quiet and clear as a valley. C major is more tranquil and solemn than the general major key.

Extended information:

In music, the intervals from the first to the eighth note of any major scale should be the same as those in C major.

So when we sing, we should feel that the distance between the intervals is the same, but the pitch is different, and no matter what major key it is, it is based on the roll call of each scale in C major. The first sound is sung as Do, the second sound is sung as Re, and so on.

This kind of singing method is known as the "first tune singing method".

Reference material: C major_Baidu Encyclopedia