What it is
It is the craft and method of structuring instructions: giving a role, context, output format, examples and constraints to cut down generic or wrong answers.
Why it matters to an agency
A well-designed prompt is the difference between an output you have to redo and one that is ready for the client. Standardizing your prompts makes your operation repeatable.
Example
Going from "write me an email" to a prompt with a role, an audience, an offer, a table format and a defined tone.
By the numbers
The base structure has 5 components: role, goal, context, format and 1 to 3 examples. That covers most agency cases without advanced techniques. Unlike fine-tuning, iterating on a prompt costs 0 dollars and takes minutes, while retraining requires data, time and budget.