"Sniffing Packets" is such a catchy little term that I had to find out what it meant so I could then use it in a conversation:
For transmission over the Internet, digital information is broken down into small chunks called data packets. They are sent from server to server until they are recombined at the destination to make a file, web page, email, picture, document, etc.
Sniffing Packets refers to the ISP practise of inspecting the information inside these Packets to weed out Torrents that might be sucking up bandwidth. But would you know if your ISP was Sniffing your Packets or throttling your bandwidth because you're using BitTorrent?
Glasnost is an application from Measurement Lab that can tell you if your ISP is Sniffing your Packets or throttling your bandwidth.