Filters are a standard feature of Odoo, available everywhere. They can be an easy way to understand domains

This is a very simple example. We will add a filter to show Quotations that are linked to an Opportunity.

Click on “Filters” and then “Add Custom Filter”. Then select the criteria – in this example that there is an Opportunity for this Quotation:

Click on “Apply” and only one Quotation is displayed:

Now we need to give this filter a name and save it:

Having saved it, the filter is shown in the list.

Enable “developer mode“, navigate to Technical / User-defined Filters and view the filter you created.

OK, yes, I used a filter to search for a filter. Type in “Opportunities” and search in “Filter Name”.

Click on the Filter to see the details:

The domain is:

[["opportunity_id","!=",False]]