What is Guidance?
In early diffusion models, generation was basically rolling dice (seeds). Assume you train a model on a dataset of elves and bunnies. While you can ask it to generate an image, you can't tell it to specifically generate an elf or a bunny. The only thing you can do is keep changing seeds, until one just so happen to appear.
Guidance is the mechanism that solves this. It is the umbrella term for the techniques used to steer the model's generating process toward a specific target.
Guidance can take many forms, from text prompts, to other input images, a hypernetwork such as ControlNet, and more.