What is the meaning of "Terumeha"?
Rashi: It is separated. Terumah is separation; Terumeha is separated. This strip will be separated for them from Terumas ha'Aretz ? the big strip separated, from the Okainus to the eastern border, 25,000 wide.
Radak: Terumah is an adjective. Its grammatical form is like Tachteha and Shelishiyah. Even though the Kohanim's portion is with the Mikdash, it is removed from Terumas ha'Aretz; it is Kodesh Kodoshim. Terumas ha'Aretz includes also the Leviyim's portion and Achuzas ha'Ir; the entire city of Yerushalayim is Terumah.
Why does it say "Kodesh Kodoshim"?
Rashi: The entire strip is Kadosh for Kohanim, Leviyim, the Nasi, Achuzas ha'Ir and those who serve the city. This is 25,000 long and 6,000 wide, separated for Kohanim and the Mikdash. It will be Kodesh Kodoshim.
Where is "El Gevul ha'Leviyim"?
Rashi: By the strip of the Leviyim. Radak ? El is like Al. It will be near the Leviyim's border. Malbim ? it is north of the Leviyim's border.