A blip or bogey was a short burst of light and high-pitched sound that indicated the intermittent presence of an object in the range of a scanner's detection.
In 1969, United States Army Technician Webb noticed a blip on a RADAR screen which turned out to be the USS Enterprise, which had traveled there from the year 2267. (TOS: "Tomorrow is Yesterday")
On the Enterprise's bridge in 2266, Spock noticed a blip on the starship's motion sensor which seemed to indicate the presence of a Romulan Bird-of-Prey; later, he noticed it had changed its heading, moving in a "leisurely maneuver." (TOS: "Balance of Terror")
In 2364, Geordi La Forge detected a bogey moving toward USS Enterprise-D at their five o'clock. (TNG: "Datalore")
In 2367, the USS Enterprise-D picked up three blips on the E-band: two originating on the ship, one on the surface of Krios. While initially attributing it to a potential protostar, it was determined that the transmission was Romulan in origin, which aided the Enterprise's crew in uncovering a Romulan plot to compel Geordi La Forge to murder Klingon Governor Vagh. (TNG: "The Mind's Eye")