It's worn in the buttonhole of a lapel, so the name of this floral accessory is French for "buttonhole"
However, we don't recommend pinning 
a flower to your lapel: a pin can poke you or easily pull a thread loose in... [DOC] [TLE] Lapel Flower & Boutonniere | Origins | History | How To Wear | NYC [PAR] Jun 26, 2013 ...