system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why does American English grammar occasionally use a comma instead of "and"?

I see it relatively often on Reddit, usually when listing things. For example, a front page thread at the moment is titled "Cyberscare: Ex-NSA chief calls transparency groups, hackers next terrorists". This makes very little grammatical sense to me... shouldn't it be "Transparency groups *and* hackers next terrorists"? Whenever I see a comma, I imagine a pause in the sentence.
gpt
It's usually used in headlines to save space. In a headline, a comma uses way less space than the word "and."

Also, in your example, it emphasizes that each item in the set is being directly and individually implicated. The Ex-NSA chief says transparency groups are the next terrorists. He also says Hackers are the next terrorists. He isn't necessarily saying "transparency groups and hackers, acting in concert, are the next terrorists." So there is more clarity than if it had just said "transparency groups and hackers are the next terrorists"