WHAT IS METATRADER?
MetaTrader is a Forex and Futures platform created by the MetaQuotes Company.  
The MetaTrader platform is supported by hundreds of brokers and is the fastest growing Forex platform with thousands of new traders joining each day.
MetaTrader is free.  When I first started using MT, some brokers added an extra 1-2 pips to the spread.  Fortunately, the fierce competition in the Forex market forced almost all brokers to remove the extra charge. 
What makes MetaTrader unique is the support of Expert Advisors.   All MetaTrader platforms, regardless of the broker, support Expert Advisors.