What are Bitcoin inscriptions (ordinals)?
Data, such as an image, written into a Taproot payment's witness and tied to one satoshi, so it lives on the blockchain.
Ordinals is a scheme that numbers every satoshi; an inscription attaches data to one of them inside a TaprootTaprootA 2021 upgrade that added Schnorr signatures and addresses starting bc1p, making complex payments cheaper and more private. input's witness. The result is a token or image that exists entirely on chain and can be sent like any other satoshi.
Inscriptions are valid payments and appear on explorers as ordinary-looking transactions with extra witness data. Whether they belong on Bitcoin has been argued since 2023; the OP_RETURNOP_RETURNA payment output that stores data instead of paying someone. It can never be spent, so nodes don't track it as spendable. relay debate is part of the same argument. Fees for large inscriptions can be high.
References
- Ordinals, “Ordinal Theory Handbook”.