An expedition is an organized journey undertaken for a specific purpose, usually involving exploration, research, or adventure in challenging or unfamiliar places. When scientists mount an expedition to Antarctica, they carefully plan months of travel and research in one of Earth's harshest environments. When Meriwether Lewis and William Clark led their famous expedition across parts of what is now the western United States in the early 1800s, they spent years mapping territory that was new to them, studying plants and animals, and meeting Native American nations.

Expeditions require serious preparation. Unlike a family vacation, an expedition means packing specialized equipment, training for difficult conditions, and planning for problems you might encounter. A mountain climbing expedition needs ropes, tents, and food for weeks. An archaeological expedition to uncover ancient ruins brings tools for careful digging and preserving artifacts.

The word suggests adventure and discovery, but also purpose and organization. You might take a hike, but you'd launch an expedition. Scientists go on expeditions to study rare animals in remote jungles. Explorers throughout history mounted expeditions to reach the North Pole, summit Mount Everest, or dive to the ocean's deepest points.

People sometimes use the word playfully for ordinary trips that feel like adventures: “We're mounting an expedition to the grocery store in this snowstorm!”