Bob wants to kiss Alice. Bob moves toward her, but at the last moment, Alice turns her face, and Bob ends up kissing her cheek instead. Generally done to show that relations between two characters are frosty. If relations are especially frosty, she may not even be that subtle. Other reasons do exist, such as to delay The Big Kiss (in which case, Alice didn't realize Bob was trying to kiss her), or because it's not the time/place for smooching. Or maybe one part of the party just doesn't want to kiss. See also Almost Kiss, for when the kiss is interrupted by external circumstances.