The term “full on chain” refers to the scenario where all activities occur directly on the blockchain.
For instance, when creating a Non-Fungible Token (NFT) on Ethereum, many NFTs store image data on a centralized server or IPFS (InterPlanetary File System), with only the location of that image data (typically a URL) stored on Ethereum. This would not be considered “full onchain.”
Conversely, when creating an NFT on Bitcoin (such as through Inscriptions), all information is recorded directly on the Bitcoin blockchain. Therefore, as long as Bitcoin continues to exist, anyone can verify the existence of this NFT at any time. In this case, an NFT on Bitcoin could be described as being “full onchain.”