"By foul craft Saruman has crossed Orcs with goblin-men, he's breeding an army in the caverns of Isengard. An army that can move in sunlight and cover great distance at speed. Saruman is coming for the Ring."
The Uruks were a species of powerful orcs that originated from Mordor. They were first seen in the attacks on Ithilien and Osgiliath in the Third Age. Saruman also used Uruks in his own army, along with Wildmen and orcs. His Uruks were able to resist the sunlight and were aided by his wizardry. It was a small group of Uruks that killed Boromir and kidnapped Merry and Pippin.