A more thorough explanation:

Definition: To assemble together troops for inspection or service, or potential troops for enlistment.

Example 1: The sergeant ordered the soldiers to muster at the parade ground for their morning inspection.

Example 2: The army recruiters mustered a group of young men and women who were interested in joining the military.

These examples illustrate the definition of "muster" as a military term used to gather troops for inspection or service, or to gather potential troops for enlistment. In the first example, the soldiers are ordered to gather for their morning inspection. In the second example, the recruiters gather a group of people who are interested in joining the military. Both examples show the act of assembling together for a specific purpose related to military service.