noun

• (astronomy) A cloud of gas and other matter surrounding and captured by the gravitational field of a large diffuse astronomical object, such as a galaxy or cluster of galaxies.
• (religion) nimbus, a luminous disc, often of gold, around or over the heads of saints, etc., in religious paintings.
• (advertising) The bias caused by the halo effect.
  "In both cases, they found that […] there was a halo effect (e.g., when a "low cholesterol" claim was made, consumers perceived other nutrients, such as fat, also to be at low levels when they were actually high). Andrews reported that these misleading halos were reduced only when the claims were accompanied by an evaluative disclosure […]"
• (art, religion, iconography) a circular annulus ring, frequently luminous, often golden, floating above the head

verb

• (transitive) To encircle with a halo.

noun

• (parachuting) Acronym of high altitude, low opening (“a type of skydiving where one leaves the launch platform from a high altitude and opens the parachute at a very low altitude”).
  "When you have enough experience, you can do a HALO jump."
• (aviation) Acronym of high altitude, low orbiting.
  "Weather balloons at maximum altitude are considered HALOs."

noun

• (informal) A member of the Angels Major League Baseball team.