Clocking in at just one word, the title of Wings sure knows how to keep it simple. But even with just one word, the title conveys a lot. For one thing, Laurel's back sprouting a blossom is one of the most important events of the book since it's what provides physical proof that something about her is different, which leads her on a quest for self-knowledge. And while the blossom is just that, a flower, it also kind of looks like wings.
Next, when Laurel starts trying to learn more about her heritage as a faerie, her Google searches bring her a lot of info about faeries having wings and pixie dust and stuff. But she finds out from Tamani that faeries don't always have wings (and that most of the other "facts" Laurel found on the internet are bunk, too). So the thing about faeries supposedly having wings comes to symbolize the human tendency to misinterpret information about faeries.
Finally, the very idea of wings on a human-looking person is imaginative and makes us think about what is real and what is not. Laurel has to confront these issues because she doesn't have a choice. It's kind of ironic that wings have whimsical connotations—faeries with wings, angels with wings, ponies with wings, yay—but for Laurel, her blossom and her faerie heritage could be a matter of life or death (like at first when she thinks the bump might be a tumor, and later when her connection to the land in Orick gets her almost killed by trolls).
Wings: They're all fun and games and sparkles until they make you question your identity and then someone tries to kill you and your family because of your connections to the faerie homeland. That about sums it up.