Some high schools, colleges, universities, and other places where students are located require any organized group of students that wishes to use school resources to hold meetings or to raise money register with a central organization. Each organization is then called "registered," meaning that the central organization is aware of its existence and has given it certain responsiblities and privileges.
One of the responsibilities for groups is to legally disassociate themselves with their education institution. Thus, the school is effectively isolated from legal disputes and direct responsiblity for the group's action. The list of registered student organizations also provides an easy way for contacting everyone who is active on campus. Some argue that the whole thing is a little bit bureaucratic.