(名詞) 可能導致人類滅絕的危險。這個字是由 existential (與人類生存有關的) + risk (風險) 拼綴而成。

“Once I identified that this is the most important thing I could do with my life, I started consciously looking for opportunities to push this X-risk ecosystem forward,” says Tallinn. He has helped start the Centre for the Study of Existential Risk and the Future of Life Institute, and contributes about $500,000 each year to research.
—Angela Chen, “Is Artificial Intelligence a Threat?,” The Chronicle of Higher Education, September 11, 2014

A Global was dominated by talk of existential risks, or X-risks. The idea is that human extinction is far, far worse than anything that could happen to real, living humans today.
—Dylan Matthews, “I spent a weekend at Google talking with nerds about charity. I came away … worried.,” Vox, August 10, 2015