system
Given the following post, respond as if you're commenting on Reddit:
human
When the news talks about how the economy is doing, they talk about the Dow-Jones and NASDAQ. What do they mean? 

Where do those numbers come from, what do they mean, why are they important to someone who doesn't have a stock portfolio?
gpt
The NASDAQ isn't actually an index; it's a stock exchange (a place where people buy and sell stocks, except that the NASDAQ is different from most stock exchanges in that it's done electronically).  The NASDAQ Composite is an index, which just means it's the average of all 3000+ stocks traded on the NASDAQ.  It exists to give you some idea of how all the stocks on the NASDAQ are doing in general.

The Dow Jones Industrial Average (often called The Dow) is the average of only 30 important companies' stock prices, so some argue that it's not as useful as the NASDAQ Composite, while others argue that it's way *more* useful because it only looks at the important companies.

A third index that should be mentioned is the S&P 500, which consists of 500 stocks hand-selected by Standard & Poor's, an organization that specializes in financial research.  Some people think the S&P 500 is the most useful because it's larger than The Dow (so it gives more information about the market, in a way) but more selective than The NASDAQ Composite (so it gives less useless information).

All three are "stock indices" which are supposed to give an idea of how the economy is doing. Since a lot of the economy is just based on how people feel (for example, people buy more if they feel like they have more money), these weird averages actually do tell us quite a bit about how the economy is doing.

Another note is that when people are investing, they tend to check how well they're doing against a stock index. If one year the S&P 500 goes up 20% and you make 30%, you're doing very well! If the S&P 500 goes up 20% and you make 10%, you're not doing so well, because you would have made more money just investing in the S&P 500 (that's right – there's a way for you to invest in an index). And if the S&P 500 goes down 30% and you only lose 20%, you've actually done well – better than the average investor.