The agents on your managed systems obtain their security content from repositories on the ePO - On-prem server. This content keeps your environment up to date.
Repository content can include the following:
Managed software to deploy to your clients
Security content such as DATs and signatures
Patches and any other software needed for client tasks that you create using ePO - On-prem
Unlike your server, repositories do not manage policies, collect events, or have code installed on them. A repository is nothing more than a file share located in your environment that your clients can access.