Block device mappings – Amazon Elastic Compute Cloud

A block device mapping defines the block devices (instance store volumes and EBS volumes) to attach to an instance. You can specify a block device mapping as part of creating an AMI so that the mapping is used by all instances launched from the AMI. … If the instance type doesn’t support multiple instance store volumes, this mapping has no …

https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/block-device-mapping-concepts.html