Investing is to put money to use, to purchase or expenditure, in something offering profitable returns. We invest money on share trading expecting to get profits. When something is done in investing and if it gives a profit, it obviously becomes a business. So, share trading is a business not at all gambling.
Intraday trading, also called day trading, is the buying and selling of stocks and other financial instruments within the same day. In other words, intraday trading means all positions are squared-off before the market closes and there is no change in ownership of shares as a result of the trades.