This is the name for a whole domain of organisms. There are three domains of life — archaea, bacteria and eukaryotes, the group that contains plants, animals and us. Archaea are single-celled organisms. And for a long time, scientists thought they were a kind of bacteria. Now, though, they know archaea are their own distinct group.
Many archaea live in extreme environments. These are places where conditions like temperature or pressure are outside what we’d find comfortable. Examples that house archaea are hot springs, under Antarctic ice and in extremely salty lakes. However, other archaea live a more luxurious lifestyle. They hang out in New York City subways, in the blue ocean depths and even on our skin.