Bessarabia is the historical region that consists of the in-game region of Bender (which in reality was just a small part of Bessarabia) AND in-game region of Bessarabia which in reality should be named Ismail/Chilia/Cetatea Alba. Ismail being the name given by the ottomans.]
Before the Russians got involved in this region, very late in the EU4 - era, Bessarabia was the traditional name of the southern plains region and only later did it become the name of the eastern region represented by Bender on the screenshot above
Wikipedia has a pretty good map of how the meaning of the names drifted: http://upload.wikimedia.org/wikipedia/commons/6/6a/Partitions_of_Moldavia.jpg