Flypaper was paper coated with a sticky, sometimes poisonous substance that was used to catch flies.
In 2266, Spock suggested that Balok's cube might be either a space buoy or "flypaper." (TOS: "The Corbomite Maneuver")
When the USS Enterprise was held by Vaal's tractor beam in 2267, Montgomery Scott described the situation as being like a fly caught on flypaper. (TOS: "The Apple")
In the second revised final draft script of "The Corbomite Maneuver", Uhura implied she was unfamiliar with the term "flypaper". Kirk tried to explain it was "a nineteenth century device" but Spock interrupted, correcting him it was more from the 20th century. Kirk continued the explanation, saying it was "a paper Earth used to use... covered with a sticky substance which trapped insects which flew into it."