Filters on some types of custom fields
From Planfix
Filters in some types of custom fields allow you to display a list of selectable values that match the conditions you set. Filters are available in the following types of fields:
Setting up a filter in a custom field
To activate a filter, you must select "Meets the conditions" for Display in selection controls in the field settings:
After you have done this, you will be able to add a set of conditions which must be met in order for values to be displayed for selection in this field: