Since I had to google I'll share the definition: IPFS is InterPlanetary File System, it's a protocol, hypermedia and file sharing peer-to-peer network for storing and sharing data in a distributed file system. IPFS uses content-addressing to uniquely identify each file in a global namespace connecting IPFS hosts. It is like a public distributed blockchain for parts of files and each file has an unique id and a hash to make sure they haven't been tampered with once you download them. When you open a node you can select which files you would like to make available for people to download from your server.
I wonder however how will IPFS prevent itself, once popular, from being either overrun by criminality such as pirating, or to be limited by the government because of that criminality, or subject to ISP blockage (like they do to the other popular peer to peer downloading service)?