Irradiation is the use of radiation from x-rays or radioactive materials to kill bacteria. It is used to sterilize food, but does not make the food itself radioactive.
The benefits of irradiating food includes the ability to control insects and bacteria, such as salmonella. The process can give foods (especially fruits and vegetables) a longer shelf life, and reduces the risk of food poisoning.
Food irradiation is used extensively in many countries. It was first approved in the U.S. to prevent sprouts on white potatoes and for the control of insects on wheat and in certain spices and seasonings.