1)
What are "Nikros ha'Tzurim"?
1.
Radak: They are caves, like "v'Samtich b'Nikras ha'Tzur" (Shemos 33:22). They are called so, for they are Menaker (carve out) in rocks and make caves.
2)
What are "Se'ifei ha'Sela'im"?
1.
Radak: They are sharp peaks of rocks. A peak resembles a tall branch of a tree. the same applies to "bi'S'if Sela Eitam" (Shoftim 15:8).
3)
What is the meaning of "Mipnei Pachad Hashem"?
1.
Malbim: It is due to fear of His punishment and awe of His exaltedness, like it says above (10).