The term whitepaper originated in Great Britain, due to the color of government-issued documents in the early 1900's.
The famous Churchill white paper of 1922 (featured above) is considered the document which gave origin to the term.
In cryptocurrency, whitepapers are supposed to be the reference technical documents for projects.
Most cryptocurrency projects will publish separate market-oriented and technically-inclined materials.
The technically inclined content is usually compiled into one or more whitepapers. Developers look to whitepapers to understand how the protocol works and how the pieces of a cryptocurrency fit together.
Perhaps the most famous cryptocurrency whitepaper of all is the original Satoshi Nakamoto whitepaper describing Bitcoin - a peer to peer electronic payments system.
Nakamoto's whitepaper precended Bitcoin's first software version by several months.
Since then, every cryptocurrency project publishes a whitepaper which explains how its value proposition is achieved by technical means.
The Ethereum whitepaper is often cited in many contemporary crypto projects, especially in DeFi.