An Orderblock / Supply & Demand is an area of price where financial institutions and banks have collated their orders, to gain enough liquidity to push price in the direction they intend. (in the direction that follows the order flow planned by them) Think of it like a foot print the banks have left behind. We have all seen large movements in price on the charts no doubt, and these large movements often leave behind clues as to what the banks are doing
http://dlvr.it/T3s0kN
