A challenge is an attempt to remove or restrict materials, based upon the objections of a person or group.
A banning is the actual removal of those materials.
Challenges do not simply involve a person expressing a point of view; rather, they are an attempt to remove material from the curriculum or library, thereby restricting the access of others. Due to the commitment of librarians, teachers, parents, students and other concerned citizens, most challenges are unsuccessful and most materials are retained in the school curriculum or library collection.
Throughout history, more and different kinds of people and groups of all persuasions than you might first suppose, who, for all sorts of reasons, have attempted—and continue to attempt—to suppress anything that conflicts with or anyone who disagrees with their own beliefs.
In his book Free Speech for Me—But Not for Thee: How the American Left and Right Relentlessly Censor Each Other, Nat Hentoff writes that “the lust to suppress can come from any direction.” He quotes Phil Kerby, a former editor of the Los Angeles Times, as saying, “Censorship is the strongest drive in human nature; sex is a weak second.”
According to the Challenges by Initiator, Institution, Type, and Year, parents challenge materials more often than any other group.