In the video game Halo 2, High Charity is the name of the mobile capital city of the Covenant. It is a large bulb-shaped structure, which is actually a massive starship. It is capable of slipstream jumps, like any other vessel. The city houses the majority of structures sacred to the Covenant, such as the chamber of the Council, the Mausoleum of the Arbiter, and the Sanctum of the Hierarchs. The power source is in fact a Forerunner ship which had been modified to power the entire city.
Before The Fall of Reach and the destruction of the Pillar of Autumn at the first Halo, the UNSC planned to have that ship transport Spartans to capture a Covenant ship, in order to locate High Charity. There, they would capture the High Prophets, and force an end to the war with a peace treaty or truce. During the events of Halo 2, however, Master Chief (who was alone teleported to that same Covenant homeworld by Gravemind) abandons this goal and decides to kill the High Prophets instead in which according to Dr. Halsey's profile on Covenant society would escalate the war. Master Chief receives aid from Marine POWS, not his Spartans this time.
During the course of the game, Flood took advantage of the chaos surrounding Master Chief's infilitration and the ensuing Covenant civil war between the Separatists' predecessors and Loyalist forces, using the situation to infest the city. Eventually the Forerunner ship at High Charity's core takes off, with Master Chief inside. Cortana stays behind. The city is abandoned and assimilated by the Flood, drifting in the middle of a space battle. Whether it will be reinhabited or destroyed in the future (Halo 3) is unknown.
