Elasticity in the AWS Cloud refers to which of the following?

 Elasticity in the AWS Cloud refers to the ability to acquire resources as you need them and release resources when you no longer need them. In the cloud, you want to do this automatically1. This means that you can rightsized resources as demand shifts, and you can easily procure resources when they are needed. Elasticity is not related to how quickly an Amazon EC2 instance can be restarted, the maximum amount of RAM an Amazon EC2 instance can use, or the pay-as-you-go billing model. These are aspects of scalability, performance, and cost, respectively2.

For more information on elasticity, you can refer to the following sources:

Elasticity - AWS Well-Architected Framework

Elastic - Reactive Systems on AWS

What is the difference between scalability and elasticity?