The season 3 episode of "Stranger Things" is titled "Chapter One: Suzie, Do You Copy?" The missing name is Suzie.
The title refers to Dustin Henderson's attempt to contact his girlfriend over a long-range radio from the hilltop near Hawkins. After returning from science camp, Dustin proudly tells his friends about Suzie, but they doubt that she exists. He repeatedly calls her using his radio, Cerebro, before finally reaching her during the season's climactic events.
Suzie is played by Gabriella Pizzolo, and the character becomes important beyond the title: Dustin asks her to recite the value of Planck's constant, which helps Joyce and Hopper open the underground Soviet machine beneath Starcourt Mall. A common mix-up is the episode number: it is season 3, episode 1, not the finale, although Suzie's radio conversation returns near the end of the season.