Poaching is just a really fancy word for illegal hunting of wild animals and plants. This happens when an animal is protected by the law, but people still hunt the animal. Found on the endangered species list pages and the home page.
Conservation is the act to protect plants, animals, or even fungi. Found on the "Who's trying to help?" page and the "Ways to Help and Conserve" page.
Pollution is the contamination of an ecosystem caused by human actions. Types of pollution include chemicals, smog, and sound.
A biological hotspot is an area with a wide variety of plants and animals and collections of extremely threatened species. Found on the "Who's trying to Help?" page.
An invertebrate is an organism with no backbone or spinal structures. In most cases, the organism would have an exoskeleton, or a hard outer shell, instead. Found on the "Story of the Endangered Species Act" page.
A cetacean is simply a confusing word for a marine mammal. Found on the "Who's trying to Help?" page.
Sources: http://animals.about.com/od/wildlifeconservation/tp/wildlifeconserv.htm ; http://en.wikipedia.org/wiki/Conservation ; http://www.encyclopedia.com/topic/pollution.aspx;