As Wikipedia defines it,
In fiction, a plot hole, plothole or plot error is a gap or inconsistency in a storyline that goes against the flow of logic established by the story's plot. Such inconsistencies include such things as illogical or impossible events, and statements or events that contradict earlier events in the storyline.

A plot hole is created by the details of the writing itself being contradictory, in a way that impacts the plot. If Harry was stated to have been born on July 30th, but then later born on July 20th, this would be an irreconcilable contradiction but not necessarily one that affects anything.

Nothing prevents Harry from, let’s say, pulling out a gun and shooting a Death Eater- but as that hadn’t been established or explained, there would be a grave loss of faith in the writing and characterization. One would start to call into question what else we don’t know, causality would lose meaning, and the plot falls apart. Yet, nothing indicates this would be impossible.

I’d call this a frayed thread- you can still wear a sweater if it’s frayed a bit, but you’ll have an irresistible urge to pick at it, or it’ll get caught on something, and the sweater will start to come undone.

Scanning discussions online, I've found that many Harry Potter "plot holes" can fit into three buckets. Errors, frayed threads, non-problems, and real deal plot holes. Errors are usually problems that have to do with dates, times, values, and other numerical details that don't add up. They also generally don't matter to the plot itself.

Frayed threads can usually be phrased as, why didn't [character] do [this]? This could be due to:
1. Implicit characterization - perhaps this is JKR’s way of telling us that the character themselves wouldn’t have thought of doing it, or been able to do it
2. Incomplete information - magic is by nature a sort of deus ex machina, and nobody but JKR can really define explicitly what the history and function of “magic” is/has been
3. Plausible deniability - an explanation exists that, while complicated, isn’t mutually exclusive with what we know

Naturally, it’s up to the reader to judge the merits of each explanation, and what those explanations imply about the overall quality of the books. That being said, the intention of this article is to be a compendium of all supposed Harry Potter "plot holes", how they can be classified, and possible explanations.