"Duck blind" is a term that originates from a method used by Earth hunters to catch their prey, ducks, off guard. The saying has also been used in reference to the 24th century method of observation using a holographic masking of a cultural observation posts used for Federation cultural observers. In cases where the Prime Directive is still in force, observations of the planet's inhabitants must be kept hidden.
A duck blind was employed on Mintaka III in 2366 by a three-man anthropology team. The power needed to maintain the duck blind required a fusion reactor with an output of 4.2 gigawatts. The duck blind failed when the reactor suffered a serious malfunction, and the observer team was discovered by the Mintakans. (TNG: "Who Watches the Watchers?")
A similar technology was employed on the Ba'ku settlement in the Briar Patch in 2375. This blind was powered by three holographic emitters, and also provided the masking fields for the team's isolation suits. The duck blind was disabled by a malfunctioning Lieutenant Commander Data after he discovered the true nature of the mission - to displace the Ba'ku from their homes, and harvest the metaphasic radiation in the planet's rings. (Star Trek: Insurrection)