Adam Back’s reusable proof-of-work concept, cited by the Bitcoin whitepaper.
Hashcash is best understood as part of a system rather than as an isolated definition. Its related coordinates show the mechanisms, incentives and historical records that give the term practical meaning.
Hashcash belongs to the documented history and social layer around Bitcoin. Primary records can establish what was published, built or decided; motives, influence and later interpretation should remain separate from those verifiable facts.
Understanding Hashcash helps distinguish a verifiable Bitcoin mechanism or historical record from slogans, products and market narratives.
For the clearest picture, read this entry together with Proof of Work, Cypherpunks, Adam Back, Bitcoin Whitepaper. The reverse links also lead from Reusable Proofs of Work, Adam Back, The Genesis Book.
Linked to related atlas coordinates
Grounded in a source record
Explains function and trade-offs
Part of the open Bitcoin knowledge graph