What does POP in POP server stand for?

After Boon's death, Watt was profoundly depressed; he and Hurley initially intended to quit music altogether. Sonic Youth invited Watt to hang out with them in New York in 1986; they recorded an outstanding cover of Madonna's "Burnin' Up" (with additional guitars by Greg Ginn) on the first Ciccone Youth EP, and Watt played bass for two songs on the Sonic Youth album EVOL.