Docker Swarm is a container orchestration tool that allows users to cluster and manage Docker containers. It is used to manage a cluster of Docker daemons and is an advanced feature for managing a cluster of Docker daemons. A swarm consists of multiple Docker hosts that run in swarm mode and act as managers and workers. The swarm manager controls the activities of the cluster, and machines that have joined the cluster are referred to as nodes. One of the key advantages of swarm services over standalone containers is that you can modify a services configuration, including the networks and volumes it is connected to, without the need to manually restart the service. Docker Swarm is built into the Docker Engine and uses the standard Docker API to interface with other tools. It is a lightweight, easy-to-use orchestration tool with limited offerings compared to Kubernetes.