Gamma rays are a form of electromagnetic radiation that were discovered in 1900 by Paul Villard. They have the shortest wavelengths and highest frequencies of all electromagnetic waves, ranging from 10-11 to 10-14 meters. Gamma rays are produced through nuclear reactions and radioactive decay. They can pass through materials like metal and concrete due to their high energy. Common uses of gamma rays include medical applications like cancer treatment, industrial applications like defect detection, and food preservation.