Password synchronization is a process, usually supported by software, through which a user maintains a single password across multiple IT systems. Provided all the systems enforce similar password standards (e.g. concerning minimum and maximum password length, complexity and re-use rules), the user can choose a new password at any time and deploy the same password across all the associated systems. If the standards vary, the user may either need to choose a password that complies with all the rules (the lowest common denominator) or this may be achieved behind the scenes within the password synchronization software (e.g. padding or truncating passwords to conform to size constraints on certain systems).
It is a type of identity management software and it's considered as easier to implement than enterprise single sign-on (SSO), as there is no client software deployment, and user enrollment can be automated.