MT4 indicator and EA

 
can any one help me what is the difference between Indicators and Expert Advisor..?
 

An indicator indicates only, it has special buffers for drawing lines, histograms etc. It cannot place or modify trades

An EA can place trades and does nor have the special buffers, but it can read from the buffers in an indicator

 
indicators are meant to show something on the chart the EA is meant to manage the trading..
Reason: