Angkor is the temple complex in Cambodia, including the iconic Angkor Wat, that is a UNESCO World Heritage Site.
Angkor was the center of the Khmer Empire, which dominated much of mainland Southeast Asia from the 9th to the 15th centuries. The World Heritage property covers a vast archaeological landscape near Siem Reap, containing temples, reservoirs, roads, urban remains, and hydraulic works rather than only one sanctuary. Angkor Wat is its most famous monument, but the complex also includes the Bayon, Ta Prohm, Banteay Srei, and many other sites.
Angkor Wat was built in the early 12th century under King Suryavarman II and was originally dedicated to the Hindu god Vishnu. Later, it became an important Buddhist temple. The Bayon, built mainly under Jayavarman VII, is known for its large carved faces, while Ta Prohm is famous for trees growing through its ruins.
UNESCO inscribed Angkor in 1992 for its exceptional Khmer art, architecture, and evidence of a powerful urban civilization. Borobudur and Prambanan are Indonesian sites, and Bagan is in Myanmar; they are not the Cambodian property named in this question.