Company tags can be set for each company you have in your contact list:
To create new company tags, go to Administration -> Codes -> Company tag and create new tags here.
The tags you create will then become available in the company window under the Company tags form.
How to use Company tags:
One way of using this function is to group vendors by their commodity. For instance:
You want to get an overview of all vendors that supply you with filters. You can then create a company tag called "Filter", tag the companies you'd like with the new tag and then you can group/filter all your companies in the company grid using the column "Tags":