Reserved Instances require an upfront payment and provide customers with a capacity reservation for a term of 1 or 3 years. They offer cost savings compared to On-Demand pricing, which is pay-as-you-go with no upfront costs. Spot Instances are an incorrect option because they allow users to purchase unused capacity at a lower price without any upfront payment or time commitment. Savings Plans also provide significant savings over On-Demand pricing, but they apply to consistent usage over a 1 or 3-year period rather than reserving specific capacity. Dedicated Hosts are a physical server with EC2 instance capacity fully dedicated to a user's use and also involve a different cost structure.