system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Can you explain how online data works and why the corporations want it?
gpt
Personal data is anything having to do with you or your interests. What colors you like, what you eat, where you work, how you look, etc etc etc. 

Corporations use this data to automatically target ads, which lets them stop using money on ads which don’t have any chance of success. 

The downside is with all that personal information, they or hackers who get access could work out things in your life and blackmail you.