system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What's "closed" in closed captioning?

Why isn't it "TV captioning" or just "captioning"?
gpt
It apparently just means that you have to opt in to seeing them (by turning them on) compared to captions which are "open" and automatically visible to everyone (perhaps on a foreign film, or something like that).