On-Demand Pricing
AWS's default pay-as-you-go pricing model, billed by the second or hour with no upfront commitment and no long-term contract.
Definition
On-Demand Pricing lets you pay for compute or database capacity by the hour or second, with no upfront payment and no long-term commitment. It's the most flexible AWS pricing model and the most expensive per unit of compute; the premium is what you pay for the ability to stop, start, or resize a workload at any time without penalty. It's the right default for unpredictable or short-lived workloads, and the wrong default for anything running continuously.
In Practice
A batch job that runs for three hours once a month is a good fit for On-Demand. A production database running 24/7 for three years is paying a needless premium and is a candidate for Reserved Instances or Savings Plans instead.