Previous studies suggest the existence of two distinct forms of laughter: mirthful/spontaneous laughter and social/intentional laughter. The current work aims to expand our understanding of the motives behind laughter and its functions in social conversation. About 1000 laughter events from 4 males and 4 females were extracted from multi-speaker conversation data, and the four predominant categories were used for acoustic analysis: mirthful, boosting, smoothing, and softening. Mirthful laughter and boosting laughter exhibit longer duration, higher F0 mean, intensity and HNR, as well as lower H1-A1 than other types, which suggest that laughter produced with positive emotion or attitude tends to have longer, higher and tenser voice quality. On the other hand, smoothing laughter and softening laughter displayed opposite characteristics, which indicates that intentional laughter emitted to smooth the interaction or soften the atmosphere can be acoustically identified to some extent from those with positive emotions. This work provides evidence that laughter with different functions has different acoustic characteristics that help us understand what laughter means in dialogue.