The Terran Accord Official Standard Reference Sustenance Cube—or Synthecube for short—is the most common form of rations in the Terran Accord! Other forms of food rations are still present but none quite as pervasive as the cube.
They were invented prior to the Terran Jump Drive, a rich investor wanted to make a food so awful that people asking for handouts would eat them and work extra hard to earn enough to eat real food. Once space travel started being a thing, their convenient stackability, high density, and ease of calculating logistics made them extremely popular.
Synthecubes are three centimeters by three centimeters by three centimeters big and each contains sufficient nutrients and hydration to cover the human body's needs for a six hour period. They are flavorless and designed to reject attempts to change that. Try to cover it in ketchup and it'll just slide right off. You can't cook them; they're unreasonably flammable.