A plug hole is where the water goes. A Plot hole is slightly different. Plot holes in long stories are gaps or logical inconsistencies in the narrative that disrupt the logical order established by the novel’s plot. Events or statements that contradict earlier events or declarations in the story fall under this category.
For example, in sci-fi/fantasy involving time travel, a protagonist can’t go back in time to prevent an antagonist/villain from being born. The earlier removal of the villain would negate any need for time travel in the first place, this being a classic time travel paradox.
Famous instances of plot holes in fiction include a little-discovered error in the first U.K. edition of Harry Potter and the Philosopher’s Stone by J.K. Rowling. On page 56, a witch complains about the price of an item being “seventeen Sickles”, yet in the monetary system of Rowling’s world, there are seventeen Sickles to a Galleon. The witch would more likely say “one Galleon”. Although this is a very minor oversight, the inconsistency was changed for subsequent editions. Clearly, an editor needs to be used in everyone’s novels.