Meaning 1:
A word used to reply to a funny message sent by someone that you're
thirsting after. It is
the ideal response if you want to seem cool and confident, because simply saying "haha" is plain and can come across as overly keen, whereas no laughter at all just makes you sound like a sociopath.
Meaning 2:
A nervous laugh. Basically used to tell
the person they're weird in a nice way.