These are the collection of targets most commonly comprise a hosts, but can also relate to other components such as network switches, containers, storage arrays or other physical or virtual components that we wish to interract with.
The inventory also provides useful information that we can use alongside our targets during the Ansible execution.
Inventories can be quite simple where they are text files with a selection of targets.
There is also an ability to create dynamic inventories where the inventory is an executable where the data being sourced dynamically.