This assumes you have already configured the aws command line tool. If not, check out my article on Getting Started with the AWS CLI.

A Task Definition is kind of like a Dockerfile or a Kubernetes deployment YAML file, in that it contains keys and values that are used to define how something should be, such as the settings for a container.

The aws ecs list-task-definitions command can be used to list the ECS Task Definitions that have been created. Something like this should be returned.

~]$ aws ecs list-task-definitions
{
    "taskDefinitionArns": [
        "arn:aws:ecs:us-east-1:123456789012:task-definition/my-task-definition:1",
        "arn:aws:ecs:us-east-1:123456789012:task-definition/my-task-definition:2"
    ]
}

The aws ecs deregister-task-definition command can be used to delete a Task Definition using the Amazon Resource Number (ARN) from the prior command.

aws ecs deregister-task-definition --task-definition arn:aws:ecs:us-east-1:123456789012:task-definition/my-task-definition:2