Shared Access Signatures (SAS) in Azure Blob Storage are time-limited security tokens that provide granular control over who can access your storage resources and what operations they can perform on those resources. SAS tokens can be created with different levels of permissions and can be valid for a few minutes to several years. By using SAS, you can grant access to specific clients with specific permissions for a specified time period, without giving them your storage account keys or making your resources publicly accessible.