How is "biodiversity" defined?

Biodiversity is commonly defined as the variety of life in the world or in a particular habitat or ecosystem. This definition encompasses not only the different species present in a given area but also the genetic diversity within those species and the variety of ecosystems themselves. By using the term "variety of life," it highlights the complexity and interconnectedness of all living organisms and their environments, which is crucial for maintaining ecological balance and resilience.

The other options, while related to aspects of biodiversity, are more limiting in scope. One option focuses solely on ecosystems, another on species, and the last one addresses genetic differences, all of which are important components of biodiversity but do not reflect the broader and more inclusive understanding represented by the correct choice.