The InterPlanetary File System is a peer-to-peer distributed file system that seeks to connect all computing devices with the same system of files … [which] could be seen as a single BitTorrent swarm, exchanging objects within one Git repository.

IPFS attempts to address the distribution problems associated with centralised (client-server) file sharing, such as HTTP. It is composed of components which implement existing concepts:

• Distributed hash tables
• Block exchanges
• Merkle DAG

Read: https://hackernoon.com/a-beginners-guide-to-ipfs-20673fedd3f

In short, content is stored on multiple machines in an IPFS system/network and referenced by a cryptographic hash of the content. This ensures content cannot be modified without detection.

Additionally, the IPNS (name system) associates an (signed) indirect link URI to a changeable IPFS address, allowing content creators to update content without needing to redistribute URIs on every change.