Variables are used to define the switch configurations in Ansible. Many Dell switches have common configurations, but there might be differences in configurations between the Dell switches based on their topological location. Variables are used to define these common configurations with group variable files or differences in configurations through host variable files. Variables are also used as part of playbook definitions, command-line arguments, inventory definitions, and so on. For more details on variables, see the Ansible documentation.
The var/main.yml file in the Dell Networking Ansible roles is used to define the common interface variables for each host, whereas the host_vars/<host_name>.yml file is used to define the variables specific to a host.