Prisoner of war

A Prisoner of War (POW, PoW, or PW) is a combatant who is imprisoned by an enemy power during or immediately after an armed conflict.

Even in the 26th Century, the UNSC continues to take prisoners of war in their conflict against the Covenant, often using them as manual labor to construct fortifications for defending against Covenant attack and digging graves for Covenant and UNSC dead. For much of the war, the Covenant refused to take prisoners, executing any human personnel who were captured or who surrendered After the discovery that only human "Reclaimers" could activate the Halo Array, the Covenant changed that policy. UNSC treatment of prisoners has been "humane," while Covenant PoW's have been brutally tortured and interrogated. After the ascension of the Jiralhanae to the positions formerly held by the Sangheili, UNSC PoW's were routinely captured and butchered for food for the Jiralhanae

The Prisoner of War Medallion is awarded to Soldiers, Sailors and Marines who have been recovered from, escaped, or released from capture by the enemy. This is the one medal that the Master Chief has not received

PoW's in the Halo Games
Though the Covenant have repeatedly been stated to never take prisoners, the games depict UNSC captives in Covenant custody multiple times. No Covenant are ever seen captured by the UNSC at all, a complete reversal from Halo: The Flood.
 * Truth and Reconciliation - Captain Jacob Keyes and several Marines are rescued by the Master Chief and a team of Orbital Drop Shock Troopers aboard the Covenant Cruiser Truth and Reconciliation. Many more Marine bodies can be seen throughout the ship.
 * Gravemind - several Marines are rescued from prisoner cells by the Master Chief, as he rampages through High Charity, following the Prophet of Truth. They are either killed by the Covenant, or infected by the Flood when it infects the holy city.Halo 2, Gravemind (Level)
 * Sierra 117 - Sergeant Major Avery Johnson and three other Marines are captured by Jiralhanae-led Covenant forces during the UNSC's extraction of the Master Chief, and used as bait to draw the Spartan into a trap. They are rescued, and manage to fend off Covenant counter-attack.