There are different ways to look at trading. One way to look at trading is in the form of intraday trading. In intraday trading, you buy and sell the share on the same day. So, you can buy the share in the morning and sell the share by evening. You can also sell the share in the morning and buy it back in the evening. Both ways it is called intraday trading. Intraday trading is for a single day. Trading is not only about intraday trading but also about any buying and selling of shares for a short period of time. For example, if you buy shares today and sell the shares after 10 days, it also called trading.
Trading means you are trying to make profits in the very short term. Short term can be a few days or even a few months. Normally, anything above 1 year is called investing and anything less than that is trading. A better way to look at trading is based on what is your intent. For example, if you are expecting that a company will get a big order and so you expect the stock price to go up sharply. As a trader, you can buy the stock and when the price goes up you can sell the stock and take away your profit.