Glossary
Negative Prompt
Short answer
A second instruction listing what you do NOT want in the image.
A negative prompt tells the model what to exclude. In Stable Diffusion it is a separate field; in Midjourney it is given with the `--no` parameter.
Its most common use is suppressing technical defects: broken hands, extra limbs, watermarks, text, low resolution.
Excessively long negative prompts do not improve results and can flatten the image. Keeping to five or ten concepts works better.
Example
Writing `--no text, watermark, extra fingers` in Midjourney measurably reduces those three problems.