All pixels have some degree of dark current leakage which is visible as Digital Imaging Artifacts: Spatially Fixed Pattern (FPN) as discussed in an earlier post of this series, Image Noise. Some pixels, however, tend to cause more dark current leakage than others. These are called Hot Pixels.
Hot Pixels are usually seen as bright colored red, orange, green, yellow, or just plain white spots, and are especially noticeable under poor lighting conditions and long exposures due to sensor heat. Hot pixels generally contribute to the overall image noise.