An oral thermometer is a common device used to measure body temperature by placing it under the tongue. However, it can be referred to by several other names including mouth thermometer, digital thermometer, clinical thermometer, and fever thermometer. The mouth thermometer denotes that it is for measuring oral temperature whereas clinical thermometer has more to do with its precision in medical settings. A digital thermometer indicates its functionality while fever thermometer directs at its intended use. Whatever term one uses to describe an oral thermometer, it remains a vital instrument for checking body temperature and monitoring one's health, especially during illness.