Noun
a short personal letter
Source: WordNetA fan sent me a letter and a $10 bill. It's a short letter - all she said was, "Hey, since it's harder for you to go out these days without getting photographed, here $10 for a pizza." I was like, "Aww, she sent me money for a pizza so I could eat at home!" Zac Efron
A short letter to a distant friend is, in my opinion, an insult like that of a slight bow or cursory salutation -- a proof of unwillingness to do much, even where there is a necessity of doing something. Samuel Johnson
drop me a line when you get there Source: Internet