What does the musical term high do mean?

In music, the term "high C" refers to the C note (also known as the C5 note) located two octaves above middle C. Because it is the highest C within the staff, it is known as high C. It appears on the fifth space of the treble clef.

High C is frequently noted for being one of the most challenging notes for singers and can be challenging for string instruments like violins and cellos to play. Due to its high pitch and the demand it makes on the vocalist, it is viewed as a demonstration of vocal skill and power.