What is the exact meaning of BTK as mentioned in the news?

Rader, 60, of Park City, entered the guilty pleas as his trial was scheduled to begin Monday. Referring to his victims as "projects," Rader laid out for the court how he would "troll" for victims on his off-time, then stalk them and kill them. "I had never strangled anyone before, so I really didn’t know how much pressure you had to put on a person or how long it would take," he told the court in describing his first killings in 1974, a couple and two of their children. Most of the victims’ relatives who were in the courtroom sat silent and stared at Rader.
     Rader was arrested Feb. 25. The onetime president of the church council at Christ Lutheran Church and Boy Scout leader, Rader admitted killing 10 people in the Wichita area between 1974 and 1991. The serial killer known as BTK -- the self-coined nickname that stands for "Bind, Torture, Kill" -- taunted media and police with cryptic messages. Sentencing was set for Aug. 25.