peer-to-peer

[#1]

Not sure what forum this should go on, so...
Just perusing my monthly usage and I noticed a sudden large chunk in the 'peer-to-peer' section.
So, what is 'peer-to-peer' and when might that crop up in my usage?
I've read the description on Wiki -- none the wiser for that! 
I don't do file-sharing, gaming, or such-like. Only one machine on the router.
It seems to have been overnight, maybe when I was on iPlayer?
Not sure if I'm just curious or slightly paranoid!
ian

[#2]

It could be iPlayer or skype, the usage section isn't always 100% accurate so some usage will likely stray into the wrong category.