IPFS stands for Inter Planetary File System, which is a protocol (rule) for how to save a file to a blockchain.
When a file is added to IPFS it is split into smaller chunks that are cryptographically encoded and given a unique fingerprint called a content identifier (CID), which acts as a permanent record of the file as it exists at that point in time.
When a file is updated, then it gets a new identifier, so any changes to a file do not overwrite the original, and files stored on IPFS are resistant to tampering and censorship.
IPFS is Web3’s answer to HTTP. HTTP downloads files from one server at a time, which is slow and expensive. IPFS works across the blockchain’s peer-to-peer network.
More information – IPFS website