I do not know whether it's called a circle, or whether it's called a halo or whatever.
But, I do know that I want to know what is the game development world term for this.
So, how do we call it?
Game Development Stack Exchange is a question and answer site for professional and independent game developers. It only takes a minute to sign up.Sign up to join this community
I would call it a Selection Indicator.
The green circle around the ship object as well as the beam and circle drawn on the ground are all part of it. The beam and circle on the ground are there to show the relative location of an object at one height with the location of an object on the ground or at a different height. It's a common strategy in 3D games, for example, Homeworld 2 made extensive use of similar drawing for movement:
Here are some Google image searches for Selection Indicator:
The blue part:
The green and red part:
The green corners:
I've found the people call this, pretty much whatever they want.