On the piano, this symbol is called "tuning".

Adding two horizontal lines means that the note is reduced by half the time value and then reduced by half, that is, the note is a quarter beat.

The horizontal line under the note is called the minus time line, which means that the time value of the note is reduced by half. The more subtractive time lines there are, the shorter the note is. Each additional subtractive time line means it is shortened to half the length of the original note.

Extended information:

The combination of sounds of different lengths produces the rhythm and beat of music, which is called the skeleton of melody. Therefore, the length of the sound is very important in music. When singing and playing music, you must master the timing of good notes.

The positions of the horizontal lines in the musical notation are different, and the durations of the marked notes are also different. The horizontal line under the note is called the minus time line, and the corresponding short horizontal line written on the right side of the basic note is called the time addition line, which means extending one beat. The more time lines there are, the longer the duration of the sound.