This guidance is primarily for customers that are running untrusted code within their EC2 instances. The "strong isolation of EC2 instances" refers to the prop

This guidance is primarily for customers that are running untrusted code within their EC2 instances. The "strong isolation of EC2 instances" refers to the properties of isolation provided by EC2's virtualization compared to processes within an operating system. It is challenging to safely and securely run untrusted code within sandboxes and processes using general purpose software. However, the hypervisor and hardware based virtualization of EC2 instances is engineered to provide isolation between mutually untrusted instances. There are several reasons that customers may want to use dedicated instances or dedicated hosts, so we provide those tenancy options as well. The most common reason customers use dedicated hosts so that they can bring their own software licenses, which are often tied to a physical host. Disclosure: I work for AWS.