1)
What is a "Nesher"?
1.
Refer to Vayikra 11:13:151:1 and the note there.
2)
What will fly like a Nesher?
1.
Rashi: The enemy, to Mo'av. Radak - Nebuchadnetzar will come quickly upon them.
2.
Malbim: The enemy will not need to delay and fight on the borders of Mo'av before entering the country. Rather, it will be like a Nesher, which flies and spreads its wings in the middle of the country. So the enemy will spread its wings on Mo'av, and immediately all of it will be under its wings.
