Cold spot is a term used to describe an unexplained area of localized coldness, or sudden drops in temperature, that are said to be the result of paranormal activity.
The temperature variances observed in cold spots is said to be the result of ghost or other spirit-like entity using up local energy (including heat) in the process of manifestation, or in order to fuel some other form of activity.
Ghost hunters often carry infrared thermometers (which can only detect surface temperatures, rather than ambient air temperatures), to detect and document the presence of cold spots in the ambient air of locations that are reputed to be haunted.  Ghost hunting organizations advise that they be checked from several different angles in order to confirm their existence and features. 
Some ghost hunters warn against using cold spots as a paranormal indicator because cold spots can often be explained by natural temperature variances. . Skeptics also commonly dismiss them, saying that it is normal for buildings to experience temperature variations. 
- Danelek, Jeffry Allan “Tools of the ghost hunting trade”, Our Curious World (2007-04-13)
- Warren, Joshua P. (2003) “How to Hunt Ghosts: A Practical Guide” Fireside, ISBN 0743234936
- Nickell, Joe (September 2006), “Investigative Files: Ghost Hunters”, Skeptical Inquirer V30#5 (2007-04-13