What is the difference between Room types and Rooms (Inventory) in Counter?

1. Room type: Is the category of the Room or group of rooms that share the same 'set up'. 
   For e.g.: Double Bed ensuite, 4-bed mixed dorm shared bathroom, etc.
   The connection (mapping) to the OTAs is always done by Room type. So, you can only have one of each room type in your property.
2. Room Inventory: Physical rooms where guests stay. They usually have a number or name to be identified.
   For e.g.: Room 1, Room 25, Room 108, Room Butterfly, Room Green, Suite 5, etc. 
   You can have different rooms per room type.

In the Image below, you can see an example in Counter. In this case, 'Room 1' is a '4 Bed Shared Dorm':