"Buy and hold" means buying something (like stock in a company) and then keeping it for a long time without selling it. It's like buying a toy and keeping it in your room to play with for years, instead of selling it right away.
When you "buy and hold" stocks, you think that the company you bought the stock in will do well over time. This means that the value (or how much it's worth) of your stock will increase over time too. This can be a good way to make money in the long run because you're not trying to guess when the stock will be worth the most - you're just holding onto it and waiting for the value to go up.
However, just like toys, sometimes stocks lose value or don't do well. If you "buy and hold" a stock that doesn't do well, you might not make much money (or even lose money) in the long run. So, it's important to choose stocks carefully and make sure you believe the company is going to do well over time before deciding to "buy and hold" their stock.