Hypercube

Hypercubes were a type of communication technology used by the Time Lords which resembled cubes. They could be used by humans as well as Time Lords, they were used by thinking or speaking to them, and were then sent through time. (EDA: Vampire Science, The Ancestor Cell) They were theoretically impossible to intercept, however an agent of the Faction Paradox was able to intercept a cube the Doctor sent to the Time Lords. (EDA: Unnatural History)

Presumably, the Doctor, seen assembling the components to summon the Time Lords about the War Lords, used a hybercube. (DW: The War Games)

Behind the scenes

In Real World science, a hypercube means a higher-dimensional analogue to a cube, the former have having four, the latter having three dimensions.