As stated in other comments and answers: you don't want "fluff" to make it longer. You want more story: an additional character with their own arc, a sub-plot with its own conflict and resolution, or get deeper into a character's flaws and how this story in particular is THE story that challenges those flaws…. More @Wikipedia
Hover over any link to get a description of the article. Please note that search keywords are sometimes hidden within the full article and don't appear in the description or title.