In nature, diversity is a source of ecosystem strength since failures are unlikely to eliminate all species. Therefore, the ecosystem will recover in some form and continue. In business or investing, diversity can provide a similar source of robustness against market instability or failures.
Specifically, when applied to a human context, diversity refers to a wide variety of cultures, ethnic groups, physical features (and race), socio-economic backgrounds, opinions, religious beliefs, sexuality, and gender identity.
The Dictionary of Sustainable Management [online] Available from: http://www.sustainabilitydictionary.com/ (accessed 8-26-16)