system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: The Dow hit 20,000. What is the Dow and what does this mean?
gpt
The Dow Jones Industrial Average (DJIA) is a weighted average of 30 large companies traded on the New York Stock Exchange.  

It is used as a rough indicator of how the stock market as a whole is doing, which in turn is a rough indicator for the economy on the whole.