Colonial Militia
From Halopedia, the Halo wiki
The Colonial Militia probably is a part-time land armed force of the UNSC used on various colonies, for example Harvest. They are inexperienced volunteers compared to the Marines, and the UNSC Army. The Colonial Militia trainees are featured in the novel Halo: Contact Harvest, along with Sergeant Avery Johnson and other UNSC Marines. Further information about the Colonial Miltia will be revealed once the novel Halo: Contact Harvest is released.