From Halopedia, the Halo wiki
The machete is a standard UNSC field issue tool for use in jungle environments. The machete's grip has a thin gel layer similar to that found on MJOLNIR Powered Assault Armor, a quad tier design to absorb shock from impacts and a unique layer design that enables the machete to self-sharpen with use.
The machete is available for use as a backpack accessory in Halo 3, added into the game in Season 6 of Halo: The Master Chief Collection. The machete is a part of the "Sword and Board" permutation, featuring the machete with a shield and a Sangheili skull - intended to emulate the Legendary difficulty sigil. During the Season 6 flight, the Sword and Board permutation featured two crossed machetes, though later in the flight and final release the model was updated to only show one, with the shield now inheriting the player's primary color. This marks the first time the machete has been seen in a Halo game outside the difficulty shield insignia.
The machete is featured as the sword found on the difficulty emblems for Normal, Heroic and Legendary difficulty in all currently-released Halo games aside from Halo 3: ODST and Halo: The Master Chief Collection, which replaces the machete with M7S SMGs and energy swords. It is given some in-universe flavor text in the menus for Halo 2's PC port alongside the UNSC shield.
During the development of Halo: Combat Evolved, a weapon bearing visual resemblance to the machete was intended for inclusion in the game. Known as the Pattern-2 Composite Sword, it is likely that the difficulty shield machetes are based upon this cut design.
List of appearances