3-of-3 in cryptocurrency refers to a multi-signature wallet setup requiring the approval of all three private key holders to authorize a transaction. This means that three separate keys are needed to access the wallet and make any changes.

Each key holder has their own private key which they must use in conjunction with the others to approve transactions. This setup increases security as all key holders must be in agreement for any funds to be moved.

In practical terms, this means that if one key holder loses their key or is compromised, the funds in the wallet will still be secure as all three keys are needed to access them. Additionally, if one key holder acts maliciously, the other two key holders have the power to prevent any unauthorized transactions.

Overall, 3-of-3 offers an extra layer of security and control over cryptocurrency funds, making it a popular choice for organizations or individuals who want to ensure that their assets are protected.