Crash just means the stocks went down in price. Stocks represent how much companies are worth. So before the crash, one share of Disney or whatever might be worth $100, then after the crash it may be worth less, like $80 a share. This is perfectly fine if you didn't buy Disney stock when it was at $100 a share. But if you had 1 share of stock before the crash, then you had $100 invested in the stock market. After the crash, you only have $80 so you just lost $20. That's why crashes are bad. However, if you only buy stock AFTER the crash, when prices are lower than before, then it's a good thing for you because then you would buy it at a low price and then the prices would go up and you would make money.
However, stock market crashes affect more than just people that own stock. The economy does badly too, so your parents might lose their jobs or get paid less or not get a raise.
We just had a crash from the Dow Jones Industrial Average at 14,000 to like 6,500. The Dow Jones is just a term people use that averages how the 30 most important companies are doing in the country. So on average, most people in the stock market would have lost about 50?f that money.
Stocks are "low" when share prices used to be worth more, and people that owned stocks when their share prices were higher have lost money.
This is the stock chart of the Dow Jones Industrial Average. As you can see on the graph, where we are right now - the point furthest to the right - seems low compared to the rest of the graph and the general up trend. Select "Max" underneath the graph if the timeline is for the day or a few months or something. You can also see around 1929 how the graph goes sharply down. That's the 1929 crash.