filter parameter declares a filter-only field and a name for that filter. A user can add filter-only fields as filters when exploring, but they cannot add them to their result set. These filter-only fields are made useful via templated filters, which are an advanced LookML topic.
The filter name must:
- be unique within any given view
- consist of characters
z(no capital letters),
- start with a letter
There are many types of filter fields, as discussed further here.
Create a filter that lets the user specify the order region: