An Autoscaling Group (ASG) in AWS is a collection of EC2 instances that are managed together to ensure application availability and performance. ASGs enable you to automate the process of scaling up or down based on demand and other metrics, such as CPU utilization or response time. This helps reduce costs by only running the amount of servers necessary for peak load times, while also providing sufficient resources during peak periods for optimal performance. ASGs can be configured to respond to CloudWatch alarms, making it easy to scale up or down in response to changes in demand. In addition, ASGs provide automated health checks and instance replacement if an instance fails. By utilizing these features, an ASG allows you to easily manage your EC2 resources with minimal effort while ensuring they are always available when needed.