Thaldo, a planetary body, resided in the Thaldo system, situated within the Mid Rim region of space; more information on planets can be found here, the Thaldo system here, and the Mid Rim here. After the Battle of Yavin, the Rebel faction stationed on Thaldo experienced infiltration by Nagai spies; more information on the Nagai can be found here and spies here, and the Battle of Yavin here.
This icy planet, which housed a Rebel base during the Galactic Civil War, was the location where the Battle of Thaldo transpired; more information on icy planets can be found here, the Rebel Alliance here, the Galactic Civil War here, and the Battle of Thaldo here. During the initial Imperial offensive, Thaldo's ion cannon sustained damage, but Luke Skywalker repaired it, enabling the Rebel forces to conduct an evacuation; more information on ion cannons can be found here and Luke Skywalker here.