"Top" means "support" or "shore up". The "o" in "Top" sounds slightly like a "u" or short "oo".
Confusingly, there are four small structures in Angkor called Prasat Top. Two of them are located inside Angkor Thom, they are called West and East Prasat Top, the latter being the Mangalartha temple or monument 486. To the east of Angkor Thom there are two more structures which are sometimes called Prasat Top, one of them is just north to Ta Prohm and south-east to Ta Keo. It is believed to be a corner temple in the former (hypothetical) capital Jayendranagari surrounding the Ta Keo. Even more confusingly, those two "Prasat Tops" outside Angkor Thom are also called "East" and "West Prasat Top", at least on Google Maps in 2013.
The fourth Prasat Top - or the eastern of the two "East Prasat Tops"! - is situated one kilometre south of Pre Rup. It is difficult to find, as it is hidden in a grove surrounded by farmland. There is not much to see at the spot, except some sandstone blocks surrounding a whole in the ground on a small mound that is left from former sanctuary.
This unprepossessing ruin of Prasat Top in the area south of the East Baray probably belonged to the group of temples built under King Rajendravarman II (944-968), the most significant one being Pre Rup, of course.
Inscriptions from the earlier period of Yashovarman I, who built the East Baray, claim that he built 100 Ashramas for several religious groups at the southern shore of the East Baray. Remarkably, the names of many Indian schools of thought are mentioned, such as Pashupatas, Tapasvins, Pancharatras, Bhagavatas, Sattvatas, and Buddhist Yashodashramas. All of them are said to have had a royal pavilion called Rajakuti. The inscriptions furthermore mention "ahimsa" (non-violence in a very comprehensive sense) and vegeterian diet, two more typical terms used for specific Indian ideas. This indicates a new wave of Indianization under Angkor founder Yashovarman I.
Under Rajendravarman II Sanskrit poetry, on some inscriptions in this East Baray vicinity, indicates even direct contact with Indians or the presence of educated Brahmins of Indian origin at the royal court.
Whover want to visit the few remains of Prasat Top, can of course do so without Angkor ticket.