pony o Share definition Flag A rubber or elastic hair tie. So named because they are used to put hair into ponytails and they look like o's. Look at Terry's new pony o. It looks exactly like the ones I got last week! pony o by don't touch my hair fatass March 17, 2005 0 0 Get merch Get the pony o mug. Buy Now — $32.95 See more merch