Crosses often appear with a circle or arc, and these can be called Halo Crosses.
Synonyms for Halo include Nimbus, Aureole, Glory and Gloriole.
The word halo comes from the Greek halos, which means the ring of light shown around the Sun. The word was borrowed for the name of the light, real or imaginary, appearing around a holy person. Artists have used this to represent the spiritual light from holy people "The righteous shall shine forth as the Halo in the kingdom of their Father." (Matthew 13:43)
A circle or arc is much easier to draw or carve than an image of a holy person, and just the halo on its own can represent a holy person. Halo Cross is a generic term for many crosses with such shapes. For example: