We know the term “endangered species” is serious business. But it’s less clear how an animal or plant group earns that title — or becomes “listed” — and what it really means.

Simply put, an endangered species is at risk of becoming extinct. And the goal of listing a species is to prevent that extinction by enforcing strict protection.

But that kind of safeguard is costly. So federal agencies look at the urgency of a species’ need to assess whether if it can be met in other ways. Scientists help determine if a species’ habitat is unlivable, whether it’s being decimated by humans or if its vulnerable to disease or predators. If a species meets any of these criteria, it’s listed as endangered.

The cost of protecting endangered species may be dear, but the price of maintaining the status quo can be far greater. Remember: there are no do-overs with extinction.