A Spot Fleet is a collection, or fleet, of Spot Instances.
The Spot Fleet also attempts to maintain its target capacity fleet if your Spot Instances are interrupted due to a change in Spot prices or available capacity.
A Spot Instance pool is a set of unused EC2 instances with the same instance type, operating system, Availability Zone, and network platform (EC2-Classic or EC2-VPC). When you make a Spot Fleet request, you can include multiple launch specifications, that vary by instance type, AMI, Availability Zone, or subnet. The Spot Fleet selects the Spot Instance pools that are used to fulfill the request, based on the launch specifications included in your Spot Fleet request, and the configuration of the Spot Fleet request. The Spot Instances come from the selected pools.