Popular fiction is the genre of fiction which is widely read in its time, for example the Harry Potter series.
Explanation:
Popular fiction as a genre came up when widespread literacy in the middle class expanded the reader base of literature considerably and institutionally legitimate literature did not appeal to the new literate readership.
The result of this was the expansion of literature into popular genres and creation of books that cater to a children audience or a middle class readership.
The great example for this sort of book is Harry Potter which captured the imagination of many children.