Prompt engineering covers how you phrase a request to a chatbot: giving context, stating the goal, showing an example of the output you want, and setting constraints like length or format. Small changes in wording can change the answer a lot.
Practical tips: say who the answer is for, break big tasks into steps, paste the source material instead of assuming the model knows it, ask it to say when it is unsure, and review the result. Bad prompts are also the most common reason a chat ends up roasted on BotDoors.