An information security management system (ISMS) is a set of policies and procedures for systematically managing an organization's sensitive data. The goal of an ISMS is to minimize risk and ensure business continuity by pro-actively limiting the impact of a security breach.
An ISMS typically addresses employee behavior and processes as well as data and technology. It can be targeted towards a particular type of data, such as customer data, or it can be implemented in a comprehensive way that becomes part of the company's culture.
ISO 27001 is a specification for creating an ISMS. It does not mandate specific actions, but includes suggestions for documentation, internal audits, continual improvement, and corrective and preventive action.