The Hill Riplah is on the east side of Sidon, and appears to be large enough, that Lehi could hide his army behind it. It is not clearly stated whether it is to the north or south of Manti, but I am inclined to place it to the south, on the basis that Moroni's armies were able to get to Manti first and then, presumably, travel further south to make preparations for their ambush. The Lamanites are said to have gone around by way of the wilderness, and this is also a wilderness that is south of Manti.
It has been noted that Jaredite names such as Ripliancum and Riplakish are suggestive of a Jaredite origin for Riplah.
In Hebrew, resh-peh-lamed, as a root conveys the ideas of "to drape", "to hover", "to overwhelm with dark clouds", "thick darkness", "heavy cloud", or "gross darkness". It can be, more specifically, the cloud that hides God's glory.
Peh-lamed-aleph, signifies "to be extraordinary", "surpassing", "beyond human power", or "miraculous".
Culturally, the most directly connected Biblical Hebrew idea would be Riblah, a location where Israel's adversaries set up a strategic fortification to control Israel during the time of Nephi, but it is hard to see how this parallels the events surrounding the Hill Riplah.
I'm inclined to think that the name is conveying the idea of a hiding place, or a covert based on the ideas associated with resh-peh-lamed and maybe peh-lamed-aleph too.