The Anaconda surface-to-air missile is a type of anti-aircraft ordnance used by the UNSC, possibly used by large vehicles (although this is only speculation).
These missiles are only mentioned once in the Halo series, during the book Halo: First Strike where the SPARTAN-IIs of Red Team recover a crate marked HIGHCOM Armory Omega during the Fall of Reach that contained six Anaconda Surface to Air Missiles and a pair of Fury Tactical Nukes; though as far as we know the missiles were never actually used. Though they might have been used against the Covenant Cruiser as a last ditch effort to save the MAC generators.
In Halo Wars, two Anaconda SAM launchers may be attached to a standard UNSC prefabricated base turret to complement the M202 XP Machine Gun with anti-air abilities. These are very successful at bringing down enemy Banshees and Vampires.