AWS Lambda is a server-less service that runs code as “functions”. That means that your code is
run when needed but there are no servers running (at least not servers that you see or manage).
This reduces cost and operational overhead.
Amazon EC2 is used for running server instances so this is an incorrect answer.
Amazon ECS is used for running Docker containers which do need to run waiting for requests.
AWS LightSail is a service that is used for running virtual instances and databases using a
simplified user interface for users who are less experienced with AWS (also at a much lower cost
than EC2).