Elasticity is a fundamental characteristic of the AWS Cloud that allows systems to dynamically allocate and deallocate resources based on demand. For a retail company, this means they can scale their inventory management system up during the high traffic of holiday seasons, and scale down during slower periods, ensuring they only pay for the computing resources they need. This is a direct application of the value proposition of the AWS Cloud, which aims to provide flexible and cost-effective solutions. High availability, while important, doesn't directly relate to the scaling advantage needed for fluctuating demands. Speed of deployment is an advantage but does not cater specifically to the scalability requirement. Lastly, sustainability is more about environmental impact and does not address the retail company's immediate need for scaling.