Petroleum coke, petcoke, abbreviated coke is a high carbon solid extracted from the deep refinery of crude oil. Petcoke is a kind of fuel which is also referred as coke. It is derived from a thermal process which is an engineering chemical process because of which the huge carbon chains get split into small chains.
Source: http://www.bcmcoal.com/blog/petroleum-coke-in-saudi-arabia-bhagvati-coal-movers-pvt-ltd/