An Ansible inventory is a collection of hosts and their associated variables used by Ansible to define the environment in which it will be running. It is usually stored as a text file with a list of hosts and their associated variables.
Example:
[web]
host1.example.com ip=192.168.1.1
host2.example.com ip=192.168.1.2
[db]
host3.example.com ip=192.168.1.3
host4.example.com ip=192.168.1.4