Used to measure the temperature of food that is cooking or cooked, two main types of thermometer are used in cookery.
A sugar thermometer is used to check the temperature of sugar when making sweets such as fudge, eg heat the sugar, milk and chocolate in a pan, bring to the boil until it reaches 116°C. A sugar thermometer is also invaluable for checking the setting point when making jams and jellies, eg boil the jam rapidly until the temperature measures 105°C on a sugar thermometer. A sugar thermometer can also be used to measure the temperature of oil when deep frying.
A meat thermometer is attached to a spike which is inserted into cooked meat or poultry to measure the internal temperature to determine whether it is cooked or not, eg insert the meat thermometer into the thickest part of the meat without touching the bone and note the temperature, refer to your recipe for specific temperatures.