A position that is open & Closed within the same day.
Intraday Trading is often known as "day trading" is the act of buying & selling a financial product on the same day such that all positions are closed before the market close for the trading day.
In simple words, if one "short" stock, which means the stock is sold which is not yet own, and then buying it back later in the same day is also intraday trading.
Traders who can take risks can work in day trading.
It looks to be easiest and rewarding, but in intraday trading one has to be very fast, alert, quick and updated.
There are certain rules which may be followed:-

• Do not put all your capital into a single stock, rather trade in fractions with small investment.
  Focus on one or two stocks at a time.
  
• Make buying & selling strategy, do not buy blindly.
  
• Make only two position at a time, if one position is closed then may go for other.
  
• Update with current news & market information informations.
  
• See the past performance of the company and the stock which buying.
  
• see the volume of that stock.
  

Intraday Trading is tightly regulated practice and one has to be updated with the market.
conclusion is that investors/traders who have no time to sit on the computer during market hours wants to get rid of this tightly regulated practice may avail the services of some good advisory companies.
advisories provides stock tips for intraday which includes enter and exit levels, stop-loss limits and targets with profitable margins.