A Friend Sweep is where one deletes all the "friends" (on social websites) that you do not need or necessarily know; such as bands and friend's friends. A FS does not include people that one would like to know better; such as recently-met people.
Myspace User trollscreamer:
"Dude, I am so sick of these pages and pages of friends on myspace; I did a massive Friend Sweep. So now I have actual friends on my friends' list."
Myspace User registeraccounts:
"Holy shit, you deleted 192 friends; now you can actually call every one of them friends..."