A cliff is a steep rock face that rises sharply from the ground or water below. When you stand at the edge of a cliff and look down, you might see nothing but air between you and the ground hundreds of feet below. The Grand Canyon has some of the most famous cliffs in America, with sheer rock walls that drop thousands of feet.

Cliffs form over millions of years as wind, water, and ice wear away softer rock and leave harder rock standing. The white cliffs of Dover in England are made of chalk, while the red sandstone cliffs of Zion National Park show layers of ancient rock like pages in a history book.

The word also appears in the phrase cliffhanger, which describes a story that stops at an exciting or suspenseful moment. The term comes from old adventure serials that would end with the hero hanging from a cliff, leaving audiences wondering whether he'd survive. Today, when a book chapter ends with the main character in danger, or a TV show ends its season with an unanswered question, that's a cliffhanger. The connection makes sense: both the physical cliff and the story technique leave you suspended in mid-air, uncertain what comes next.