Transition

Transitions are commonly used for hover, focus, expansion and state changes. They differ from keyframe animations because they normally react to a change between states. In practical terms, Transition belongs to the presentation and layout layer. Knowing that layer is important because it tells you what the term can change, what it cannot change, and where to look when something behaves unexpectedly.

The common mistake is to use Transition as if it also meant Animation. That blurs two separate decisions and usually sends troubleshooting in the wrong direction. A better test is practical: A transition needs a property whose value changes; it does not create states by itself.

In day-to-day work, Transition matters when the concept needs to be identified precisely instead of being grouped with a nearby term. The practical value is not the vocabulary itself; it is being able to identify the right control, file, setting or decision when the concept becomes relevant.

transition: opacity .2s ease animates the change between an old and new opacity value when state changes. That example is useful because it turns the definition into something you can recognize, test and discuss with other people working on the same project.

Use these references when you need documentation-level detail, specifications or product-specific behavior beyond the plain-English explanation above.