A Cloud Access Security Broker (CASB) is a security solution that sits between an enterprise's on-premises infrastructure and its cloud-based applications and services. It helps to secure the use of these cloud-based services by providing visibility, control, and protection for data in the cloud. A CASB can help to identify and remediate data-loss events by monitoring the use of cloud-based services, identifying unusual or suspicious activity, and alerting the appropriate personnel when necessary. It can also help to prevent data loss by enforcing policies to control the access and use of data in the cloud, and by providing encryption and other security measures to protect data in transit and at rest.