Cervical caries is tooth decay located around the neck, or "cervix" of the tooth (hence the term "cervical").
Cervical burnout refers to the appearance of a dental x-ray when it is either over-exposed or over-developed. This phenomenon causes the x-ray image of the cervical area of the teeth to appear darker, and may be confused and mis-interpreted as cervical decay. However, because cervical burnout is the result of the way the film emulsion is exposed or developed and does not reflect any true characteristics of the teeth themselves, it represents an x-ray "artifact".