This is a POV in which the narrator can see into the mind of any character. The story can jump from place to place and from person to person, and the author has complete control of the scene and the freedom to move through the story at his/her own discretion.
Third person omniscient is a very tempting manner in which to write, however this POV should come with a warning. If not enacted with precision and acute awareness of how this omniscient voice can control the story, the work can seem disjointed and inconsistent.
Often, the best use of third omniscient is when the author has given the narrator a specific agenda. For example, satires work very well in omniscient, with Douglas Adams’ as a perfect example. In The Hitchhikers Guide to the Galaxy, the reader predominately follows the story of Arthur Dent, but the narrator also dips and out of Non-Arthur Dent related scenes for comic effect.
Essentially, when using third person omniscient be very aware of where you are taking your reader story what you’re trying to say.