What is a CSS transition?

A CSS transition is fundamentally a way to create a smooth change between two states of an element, which is why this answer is correct. When you apply a transition to a CSS property, it enables a gradual change from one value to another over a specified duration. For example, if you have a button that changes color when hovered over, applying a transition will allow that color change to happen smoothly, enhancing the visual experience for users. This can involve various CSS properties such as opacity, background-color, or transform, among others, allowing developers to create dynamic and engaging interfaces.

The other options describe different concepts in web design. Creating a hover effect can indeed utilize transitions, but this is just one application of what transitions can do; hence, it doesn't capture the full definition. Multi-column layouts refer to a different CSS technique for organizing content, while changing text color is a specific styling action that may involve property changes, but it doesn't encompass the broader nature of transitions. Therefore, option B correctly identifies the essence of what a CSS transition is designed to accomplish.