Self-sovereign Identity (SSI) is a model for managing digital identities in which an individual or business has sole ownership over the ability to control their accounts and personal data. Individuals with Self-Sovereign Identity can store their data to their devices and provide it for verification and transactions without the need to rely upon a central repository of data. With Self-Sovereign Identity, users have complete control over how their personal information is kept and used.
In all models of identity management, a digital identity requires identifiers, which ensure the user is who they say they are. However, with Self-Sovereign Identity, identifiers do not need an intermediary. This means that a user’s Self-Sovereign Identity can be registered to a claim, such as a block on a blockchain. The person can then share that identifying data when making a transaction with a bank, for example.
With Self-Sovereign Identity, a person can enter an app on their phone where their identity data is stored, then use an identification number and identity information to verify who they are. Self-Sovereign Identity adds security and flexibility to the user and allows them the ability to share data only when they choose.
Source: https://www.techtarget.com/searchsecurity/definition/self-sovereign-identity