A Token is a unit of data used by large language models. Tokens used to be pretty analogous to 3-6 letters of English text, but things have become more complicated with the advent of multi-modal generation

Large language models are usually priced on MTok or “million tokens”. You’ll often see LLMs priced at $X/MTok for input and $Y/MTok for output.

A harness is a program that interfaces with a large language model and provides it tools and context to achieve a goal. Codex and Claude Code are good examples of harnesses.

What exactly all of this accomplishes is not something I can answer for you :)