Halos are fictional megastructures and superweapons in the Halo video game series. They are alternately referred to as "Installations" by their AI Monitors, and are collectively referred to as "the Array" in Forerunner logs.

The Halos are seven ring-shaped, habitable megastructures that exist in the Halo science fiction series. The Halos resemble Larry Niven's Ringworld concept in shape and design, while they are closer to Iain M. Banks' Culture Orbitals in terms of scale and structure, the latter of the two being the inspiration for the Halo rings. While the diameters of Niven's Ringworld and Banks' Orbitals are in the millions of kilometers, each Halo is only 10,000 km (6,200 miles) in diameter, slightly smaller than that of Earth. Each Halo orbits a planet, the Ringworld concept of encompassing a star (similar to a Dyson Sphere or Dyson Swarm) being impractical for something of Halo's size in this universe.

The Halo installations were built by the Forerunners, a fictional civilization within the series, to contain and study the Flood, a rampantly infectious alien parasite. To this end, each Halo possesses a network of underground structures, ranging from laboratories to containment areas. Each installation shown in the series has a Monitor, an artificial intelligence construct, to oversee automated installation functions, such as defense and climate control. 343 Guilty Spark, for example, runs Installation 04.

The main purpose of the Halos is to stop the Flood should they multiply beyond a containable level. To accomplish this, each Halo is equipped with a super-weapon capable of destroying all bio-mass of sufficient size to sustain the Flood within a radius of 25,000 light years (roughly one fourth of the Milky Way Galaxy's diameter).