What does 4 flats in the key signature mean?

In music notation, having 4 flats in the key signature indicates that the piece is in the key of E-flat major. The flats are placed on specific lines or spaces of the staff, representing the notes that are consistently lowered by a half step throughout the piece. In the case of E-flat major, the flats are B-flat, E-flat, A-flat, and D-flat. This key signature simplifies the notation by indicating which notes are flat without having to notate them individually throughout the score.