From OpenStreetMap Wiki
|man_made = pillar|
|Used on these elements|
|Tools for this tag|
|This tag page is a stub. You can help OpenStreetMap by expanding it.
Similar pages for structural reference: Tag:railway=tram, Tag:waterway=dock.
|This tag currently lacks meaningful documentation. Pillars for bridges are tagged using bridge:support=*.|
man_made=pillar - a tag, which is proposed to tag pillars. Usually pillars are part of bridges.