The process of defining a collection of hosts to Ansible is named the inventory. A host can be defined using its fully qualified domain name (FQDN), local hostname, and/or its IP address. Since Ansible uses SSH to connect to the hosts, you can provide any alias for the host that the machine where Ansible is installed can understand.
Ansible expects the inventory file to be in an INI-like format and named hosts. By default, the inventory file is usually located in the /etc/ansible directory and will look as follows:
athena.example.com [ocean] aegaeon.example.com ceto.example.com [air] aeolus.example.com zeus.example.com apollo.example.com