A spoon is a fork in the blockchain that transfers all balances to a new native cryptocurrency.
For example, a spoon was created on Ethereum to launch the Cosmos bridge. The Cosmo bridge transferred all ETH balances to the utility token ATOM.
Spoons allow the users of the original blockchain to participate while adding new features to a project.
They are far less contentious than the more common hard fork, which completely splits off from the original blockchain and uses the same token. This fork is intended to divert users away from the existing blockchain.
Spoons are more collaborative, building on the original blockchain. They allow existing users and developers to engage in the new additions.
Ethereum is the most common protocol for spooning, and several projects seek to make it more efficient or add specific functionality without splintering off of the Ethereum Mainnet.