Physical vs Logical resources

Logical ID The logical ID must be alphanumeric (A-Za-z0-9) and unique within the template. Use the logical name to reference the resource in other parts of the template.

Physical ID A physical ID, which is the actual assigned name for that resource, such as an EC2 instance ID or an S3 bucket name. Use the physical IDs to identify resources outside of AWS CloudFormation templates, but only after the resources have been created. Eg EC2 in the console