Flames came around a little while ago. They work like trails, that are made up of small particles, which can be customised into different shapes.
The first flames were forged and introduced into the market a little while ago and were considered very rare.
A little while after this Flame Forger was introduced, the user would pay a $25 a month fee to be able to forge flames. A flame would cost around 80K - 100K to forge.
A little while ago, the flame forge subscription was removed, basically it didn't require a dollar charge to forge, I don't know if this is still the case.
You can, forge your own by pressing ctrl + L in-game or you can buy from other users in the Flames sub-forum in the Market or from the ToriMarket.
Hope this helped.