This chapter introduces Large Language Models (LLMs) and the concept of model size. We will begin by defining what an LLM is and its fundamental purpose in processing and generating human language.

You will learn about the core building blocks of these models: parameters. We will explain what parameters represent and why they are the standard metric for measuring the size of an LLM. This includes understanding common units like billions of parameters ($B$). Finally, we'll look at examples of different LLMs to provide context for various model sizes you might encounter.