What is AI? I've only heard of LLM.
AI is "artificial intelligence". That's a pretty intentionally vague term. It doesn't imply any specific technological implementation, but it does imply the device/software makes decisions autonomously that would otherwise need a human to intervene. There's a million holes in that definition, and that's why the adjective "AI" kind of sucks when used on its own. It's also worth noting it's been used in sci-fi for eons. It's also been used to describe non-playable characters in video games for a long time, which obviously didn't have the sort of "AI" we think of now.
LLMs are neural networks that work with "tokens" from text. So a big statistics-based predictive AI. There are more complex implementations that can consume other kinds of content as well, but "LLM" almost always refers to a neural network that consumes small chunks of text called tokens, and outputs more tokens based on that input. The magic we see with LLMs happens because given enough data, language itself builds up a surprisingly good model of "thinking".
There's some really good explanations in the sibling comments! I'm no expert, and I think someone can probably correct me here if I messed up something there.