In time management, gold plating is the phenomenon of working on a project or task past the point of diminishing returns.
For example, after having met a project's requirements, the manager or the developer works on further enhancing the product, thinking that the customer will be delighted to see additional or more polished features, beyond that which what was asked for or expected.
In this case, 'gold plating' means the addition of any feature not considered in the original scope plan (PMBOK) or product description (PRINCE2) at any point of the project.
This is because it introduces a new source of risks to the original planning such as additional testing, documentation, costs, or timelines.
However, avoiding gold plating does not prevent new features from being added to the project; they can be added at any time as long as they follow the official change procedure and the impact of the change in all the areas of the project is taken into consideration.