All about SS501 더블에스오공일)...

SS501 (더블에스오공일) is a popular South Korean boy band. All the members of the group have subsequently left DSP Entertainment to different management companies, but they still intend to stay together as SS501. The name of the band is a combination of letters and numbers that have special meaning. The first “S” stands for “Superstar". The second “S” is an abbreviation for "Singer". The combination of 5, 0, and 1 symbolizes "five members united as one forever".
^{They had conducted their very first Persona Concert at Seoul,2009.}
http://ss501.dspenter.com/main.asp