CubeSat
"CubeSats are a class of research spacecraft called nanosatellites. CubeSats are built to standard dimensions (Units or “U”) of 10 cm x 10 cm x 10 cm. They can be 1U, 2U, 3U, or 6U in size, and typically weigh less than 1.33 kg (3 lbs) per U." (National Aeronautics and Space Administration 2018)
Sources
National Aeronautics and Space Administration. Page Last Updated Feb 14, 2018. https://www.nasa.gov/mission_pages/cubesats/overview.