Recently a question came up about changing point-of-view in a story and how was that different from head hopping?
The two are very different.
First of all, you need to know your points-of-view. I taught them to 7th graders and you can easily find scads of resources online that teach how to identify 1st, 2nd, and the three forms of 3rd person points of view in narration (objective, limited -- only from one character, and omniscient). As writers, we play with these, to see which one is the best for telling our stories.
It gets a little trickier in analyzing when and why authors change points-of-view when writing in 3rd limited, but generally it's to show or reveal another character's perspective, because that character has knowledge / experiences that will provide a window for the reader to better understand or deepen the story's emotional impact.
There's nothing that says an author has to "pick a POV and stick with it." Authors frequently mix the types of points-of-view they use in their texts. For example, you write the bulk of a story in 3rd-limited POV from your main character's perspective, but between chapters you include journal-style 1st-person POV entries that reveal the perspective of a character who died a long time ago, say a grandparent in WWII. This is perfectly accepted storytelling technique. You see it a lot in mysteries, where the author uses it to increase tension, reveal the culprit's plan, etc. It's common in spy thrillers, where the author switches back and forth between characters to keep the reader guessing, who can I trust? It's common in adult literature as well, where authors will have huge casts of characters and use their individual stories to tell a much larger tale (can anyone say, Game of Thrones?).
So what's the difference between that and head-hopping, something readers will complain about because it causes considerable confusion?
Head hopping is when the author slips, often without consciously doing or / knowing it, into the head of another character while writing and takes the reader with him or her.
Example: Jay is a mighty warrior, and the whole story has been told from his 3rd, limited POV. Jay's fighting in a bloody battle, his axe slips from his hand, he ducks and rolls and slaps his hand on the ground blindly, searching for it. The next line is a descriptive passage from someone (you're not sure who) standing up on the balcony watching the battle. He describes the panorama of the horrors of war, of the battering ram about to breach the gates, how all hope is lost ... Huh? Whoa -- what happened to Jay? DID HE EVER FIND HIS AXE??
Sometimes it's not this obvious, but you get the point.
Reading 3rd limited POV, with shifts, is perfectly fine if the author uses a clear, consistent signal. Rick Riordan uses a chapter title with the POV character's name. It's used consistently, throughout all his books.
Deron Hicks, who writes MG mysteries (read my reviews here and here), uses breaks of white space between POV characters. That's all that's needed and it's quite effective. I've seen three asterisks *** and other creative cues used to switch POV.
The point is, if you do it once, do it throughout the piece exactly the same way, and your reader won't have a problem. If you slip...watch out! That's head-hopping. And frequently it takes your alpha or beta reader to catch it in your story.
