1.Third person omniscient is when the narrator seems very much like the author, knowing everything that happens and why it happens (though not necessarily telling everything he or she knows), able to see into the minds and hearts of all the characters.
2.Third person objective is when the narrator does not look into the mind of any of the characters or explain why any of the characters do what they do. The narrator describes events only from the outside, leaving it to the reader to draw conclusions from the details and dialog provided.
3.Third person limited is when a narrator is omniscient in some areas or to some extent, but is not completely all knowing. Typically, the narrator knows everything about one character, and tells the story from that character's perspective while not being able to see into the minds of other characters (limited).
Hope this helped, good luck!!