TACPAD
From Halopedia, the Halo wiki
The TACPAD[1] is a piece of United Nations Space Command equipment. It is a hand-held tactical database system used for analyzing and displaying combat information. It is most often used by NCOs and pull up maps of the local area and display images.[2] It might be related to a small hand-held computer, or "Data Pad".
One UNSC Marine stated: "How the foxtrot does it track anything? Whatever—I guess that’s why I carry an em eh five instead of a TACPAD." in reference to a Covenant Plasma Pistol's tracking feature. This comment indicates a TACPAD might also be used for "tracking" a target, but not for actually engaging it.
