The Universal Catalog (UC) is a classification system to designate galaxies in the Universe. It was devised by the USR in 200416 to keep track of every galaxy in the universe. It is similar to the M and NGC catalogs used on Earth.
Each sub-catalog is designated with a letter combination (A, B, C, ... AA, AB, AC, etc.), which contains a list of 9999 galaxies, each galaxy designated with a number from 0001 to 9999.