A more thorough explanation:

A genus claim is a type of patent claim that falls under the category of generic claims. It refers to a claim that covers a broad range of variations or species within a particular class or category of invention.

For example, a genus claim for a pharmaceutical invention may cover a class of compounds that have a similar chemical structure and function, rather than a specific compound. This allows the patent holder to protect a range of potential variations of the invention, rather than just one specific embodiment.

The phrase "genus nunquam perit" is a Latin term that means "the class never perishes." It was historically used in reference to a quantity of goods that were contracted for within a certain class, rather than a specific item. This meant that the destruction of some of the goods within that class did not discharge the seller's obligation to provide the remaining goods.

Overall, a genus claim is a useful tool for patent holders to protect a broad range of potential variations of their invention, rather than just one specific embodiment.