Gastronorm is a European sizing system for food containers built around a full-size 1/1 pan measuring 530 × 325 mm. Smaller pans are fractions of it, such as 1/2, 1/3, 1/4, 1/6 and 1/9, so a combination of fractions always fills the same opening. Pans come in several depths and in stainless steel, polycarbonate and other food-grade materials.
Because the sizes are standard, the same pan can go from the cooking oven to the blast chiller, into a refrigerator on GN-compatible runners, and onto a prep table or buffet well without the food being transferred. That saves time, reduces handling and lowers the chance of contamination. When buying refrigeration, check whether shelves or runners accept GN 1/1 or GN 2/1, and which pan depths the top wells take.
A hotel banquet kitchen in Jaipur might cook paneer makhani in GN 1/1 pans, blast chill them in the same pans, store them on GN runners in a reach-in, and reheat and serve them in a buffet line, all without decanting.