Ask HN: How does AI understand what I write?

I get generative AI. I understand the concept of an LLM and how it generates text. AI output processing seems relatively clear to me.

What I don't understand is how ChatGPT (or whatever) understands what I write. No matter how I phrase it, or how subtle or abstract the point or problem is, AI usually always figures out what I mean. I am mystified and constantly amazed at AI input processing.

What mechanism is at work here? If I want to deep dive on how AI understands meaning, what technology or concept do I need to research?