Each security is assigned with a unique series of letters for trading purposes which is known as stock symbols or security ID or security code or simply ticker. They help us to identify a stock, ETF, mutual fund, bond or any other security traded. On NSE, stock symbols are alphabetical characters, while on BSE, stocks are assigned a 6 digit numerical code in addition to a stock symbol. Needless to say, stock symbol or ticker is unique to each stock.  

Stock symbols are used by traders dealing in stocks to quickly locate the price ticker of the stock. Also, price movements and volume changes can be efficiently tracked using the stock symbol, as it saves time and captures a specific stock at the right time.

E.g. Stock symbol for Reliance Industries Limited (RIL) on BSE is 500325 and on NSE is RELIANCE.