AWS RedHat Enterprise EC2 Billing Confusion

According to faq https://aws.amazon.com/partners/redhat/faqs/

Whether it is on demand of spot instances

Red Hat Enterprise Linux on Amazon EC2 is offered at either a flat, hourly rate with no commitment (On-Demand or Spot Instances) or through a one-time, upfront payment (Reserved Instances). Both purchase options include Amazon EC2 compute charges and Red