| +/- highway=road
Road with unknown classification.
Road with an unknown classification. This tag should be used temporarily until the road has been properly surveyed. Once it is surveyed the highway tag should be changed to record the appropriate classification.
It implies FIXME
When this tag is used it implies a FIXME. So you do not need to add a todo=FIXME, fixme="Unknown classification", etc. It's just duplicate work for the next person to change the highway type AND remove the fixme tag.
Roads with no name
Often this tag is used also in case the road most likely has a name, nonetheless the survey done hasn't properly determined what it is, or no survey was done at all. If the road indeed has no name, that is survey has determined that there are no signs indicating its name, etc., then see this proposed feature to indicate the road has no name.