You may have heard the phrase "purple prose," thrown around, and likely in a negative way. This is because it gets downright irritating for readers.

In short, purple prose is the overuse of flowery language. It's an easy trap for writers to fall into: we're all told to be descriptive and make use of the five senses in order to engage our readers; but when you do that too much, it has the opposite of the intended effect and bores the reader to death.

The stalwart young brunet ran his willowy, sinuous fingers through his delicate, overly long, straw colored locks, ushering them out of his shining topaz pools. A crystalline orb formed on his rose cheek, and slowly danced its way over his sun darkened, yet still silk smooth, skin.*

Okay, first off, I need to go wash my brain with bleach after writing that. It caused me physical pain. Other than violating my boys don't cry rule, it's just plain bad writing. But what makes it bad is the overuse of adjectives, metaphors, and inaccurate verbs. And those are what make up purple prose.

Let us examine it piece by piece.

The stalwart young brunet: It is okay, on occasion, to refer to a person by an attribute, but most people who do so do it far too often. In this case, given the onslaught of adjectives that's about to happen, it's bad. Much better would be to simply refer to the guy by name: Jack.

ran his willowy, sinuous fingers: why two adjectives to describe Jack's fingers when the sentence is about how he's running his hand through his hair? It doesn't paint a picture, it just distracts from what's going on.

through his delicate, overly long, straw colored locks: see the previous problem, amplified. You should never need that many adjectives, especially when you end on a synonym—it's hair. Locks can be used, but when you combine it with the previous three descriptors, it's just ridiculous.

ushering them: he did not usher them. He did not have a flashlight and they weren't in a dark theater. He didn't show them where to sit. The verb works, technically, but the more you think about it, the sillier it seems, especially when combined with the billion adjectives that we've already encountered.

out of his shining topaz pools.: Eyes are the most often purple-d feature. They aren't orbs. They aren't pools. They aren't gems. They're eyes. But if you've already described them as being a gem (topaz, in this case) then you're also mixing a metaphor by immediately declaring them pools. They would be topaz-colored pools. And shiny ones, apparently. Anyway, the net effect is the same: it's stupid. So again: adjectives can be good, but the adjective + metaphor combination is not.

A crystalline orb: If I had not written this myself, I would have no idea what the hell that means. Again, it's a metaphor, but it's not a clear one. If your writing isn't clear, your reader will be confused, and that makes for a bad story.

formed on his rose cheek, and slowly danced its way: Tears do not know how to dance. Bad verb choice. The rose cheek would be forgivable, if not for the rest of the paragraph making it look bad. (Also, technically speaking, the tear would form in his eye, not on his cheek.)

over his sunk darkened, yet still silk smooth, skin.: Again: adjectives. Stop. Enough is too many, already. They hurt when you see so many in a row.

Obviously, this shows up the most often in mediocre romances—especially, but not limited to, in Mary Sue stories. It can show up in other forms of stories as well, but it's infamous in romances, both professional and fanfic. And purple prose does not a good description make.

Finding a happy medium for description is difficult; believe me, I know. But better to skimp and make it effective when you do use it, than to make your readers' eyes glaze over as they try to sort out which adjective goes with which metaphor goes with which synonym. Just say no.

* Translation: "Jack ran his hand through his light brown hair to get it out of his eyes, and began to cry."