The real time information about trades, quotes, pricing, and volume provided by exchanges, Dark Pools, and Liquidity Providers. This information is often under license from exchanges and/or market data providers. It has three typical models refered to as Level 1 (L1) for top of book price (best bid / best ask). Level 2 (L2) for full depth of orderbook and Level 3 (L3) which are all messages from the market in raw unstructured format. Market data is required by trading applications to make real-time price based decisions for execution, risk and positions.