FAT TOM is a mnemonic device that is used in the food service industry to describe the six favorable conditions required for the growth of foodborne pathogens. It is an acronym for food, acidity, time, temperature, oxygen, and moisture.

 F FoodThere are sufficient nutrients available that promote the growth of microorganisms. Protein-rich foods, such as meat, milk, eggs and fish are most susceptible.
 A Acidity  Foodborne pathogens require a slightly acidic pH level of 4.6-7.5, while they thrive in conditions with a pH of 6.6-7.5. FDA regulations for acid/acidified foods require that the food be brought to pH 4.5 or below.
 T Time Food should be removed from "the danger zone" (see below) within two hours, either by cooling or heating. While most guidelines state two hours, a few indicate four hours is still safe.
 T Temperature
Foodborne pathogens grow best in temperatures between 5°C to 57°C, a range referred to as the temperature danger zone (TDZ). They thrive in temperatures that are between 21°C to 40°C.
 O Oxygen Almost all foodborne pathogens are aerobic, that is requiring oxygen to grow. Some pathogens, such as Clostridium botulinum, the source of botulism, are anaerobic and do not require oxygen to grow.
 M Moisture
Water is essential for the growth foodborne pathogens, water activity (aw) is a measure of the water available for use and is measured on a scale of 0 to 1.0. Foodborne pathogens grow best in foods that have aw between 1.0 and 0.86. FDA regulations for canned foods require aw of 0.85 or below.

Interesting article from Restaurant Management.