A more thorough explanation:

Definition: Prior-user right is a legal right that allows the first inventor of a product or process to continue using it even after someone else has patented it. This right is designed to protect the interests of the original inventor in most countries where a first-to-file system is in place.

Example: Let's say that John invents a new type of engine for cars and starts using it in his own vehicles. Later, Tom also invents a similar engine and files a patent for it. In this case, John may still be able to use his engine even though Tom has a patent for it, thanks to the prior-user right.

Explanation: The example illustrates how the prior-user right works in practice. Even though Tom has a patent for the engine, John can continue using his own engine because he was the first to invent and use it. This right protects John's interests and prevents him from being unfairly penalized by the patent system.