What is the key difference between a shader and a material in Unity?

The key difference between a shader and a material in Unity lies in their roles within the rendering pipeline, which the correct answer highlights effectively. A shader is a set of instructions that determine how an object is rendered on the screen, providing the necessary calculations for visual effects like color, lighting, and texture mapping. In contrast, a material is an asset that uses a shader and defines how it interacts with the object's surface by specifying its properties such as color, texture, and transparency. The material acts as a wrapper around the shader, allowing developers to adjust the shader's parameters without needing to modify the shader code itself.

This distinction is crucial because it underscores that while a shader dictates the visual effects and how they are rendered, the material serves as the interface for these effects, allowing for a more versatile and user-friendly asset management system in Unity.