Rashi citing Menachem: Nechilos, Alamos, Gitos and Yedusun are all musical instruments. The tune for each Mizmor was according to the proper instrument.

Rashi citing Shocher Tov 8: Nechilos it is an expression of Nachalah (inheritance ¹ ).

Rashi: Perhaps they are troops, like [a swarm of] bees is called Nechil, and Targum Yonasan of "Nachalei Veliya'al" (Shmuel II, 22:5) is Si'as Chayavin.

Radak citing Rav Hai Gaon: This is like a swarm of bees, which is called Nechil. The tune resembled buzzing of bees.

Rashi: It is a Tefilah due to enemy troops that come against Yisrael; it is said for the sake of all of Yisrael.

Radak: Also this Mizmor was due to David's enemies within Yisrael, i.e. Do'eg and Achitofel (Shocher Tov).

Malbim: This Mizmor is divided into two parts. Until verse 9 explains how Tefilah should be, and how one who prays to Hashem should feel. The second part is a request that Hashem make him rest in Magelei Tzedek (23:3), and save him from his haters.