Hardpoint

A Hard Point is a point on the outer hull of a warship where another vessel of similar size and density may dock and link systems. These points can be used to combine engine power, telemetry, stabilize, and link computer or A.I. systems.

Background
Newer UNSC warships have these hard points on their dorsal and ventral sides, in case the ship was too crippled to move under its own power. Another UNSC vessel could then use its own hard points to dock with the wounded ship, link systems and carry it away (presumably to a repair platform or safe zone). Most likely the "hard points" on a UNSC warship are magnetic clamps or large airlocks on the outer hull on the sites mentioned.

Some Covenant ships also have hard points that can be used by a ship too large to fit inside one of the docking bays, like the Phantom.

Trivia

 * They are first mentioned in Halo: First Strike, when Cortana used the captured Covenant Flagship Ascendant Justice to dock with the disabled and abandoned UNSC Gettysburg. Since Covenant and UNSC systems are incompatible, Cortana used the Gettysburg's service drones and the Ascendant Justice's Engineers to adapt their power uplinks. It was also the first time that a Covenant and UNSC ship had touched each other without violent intentions.