The filter id. The one you get when you call a filter method that starts with apply.
// Remove spatial filter on layer 3
JMap.Map.Filter.removeByFilterId("spatial-3")
// Remove attribute filter on attribute id="on_off", on layer 4
JMap.Map.Filter.removeByFilterId("attribute-4-on_off")
JMap.Map.Filter.removeByFilterId
Remove the filter on the map following the filter id passed in parameter.