Short for "rationed food." In this case, they specifically refer to combat rations supplied to soldiers in the field. They are designed to have a long shelf life and high nutritional value. During World War II, food that was packed in jars and cans, dried, or condensed was the norm. Canned food was invented in 1804 when Napoleon offered prize money to anyone who could device a new way to preserve food for military use.
With the addition of combat stress platoons to military forces in the new millennium, the mental health of soldiers started to come into question. As a result, rations began including food that actually appealed to soldiers. The types of rations diversified and flavor markedly improved thanks to the use of retort pouches, vacuum-packing, and freeze-drying.
Multinational forces of the 21st century have rations that vary by nation so that their soldiers can enjoy food that reminds them of home.
Rations made since the Outer Heaven Uprising in 1995 have a noticeably improved taste and do a better job of promoting stamina recovery.