Notoriously double-edged: meant as a simple, low-key friendly smile, but in text it frequently reads as passive-aggressive, sarcastic, or 'I'm annoyed but being polite about it,' especially among younger users replying to something they didn't like. It was one of the last basic smileys added, arriving in Unicode 6.1 (2012) to round out the core face set.
Keywords: face, happy, slightly, smile, smiling