To expand means to become larger or to make something larger. When you blow air into a balloon, you expand it. When a business opens new stores in different cities, it expands its reach.

Expand can describe physical growth, like how your lungs expand when you take a deep breath, or it can describe ideas and knowledge. A teacher might ask you to expand on your answer, meaning to add more details and explain your thinking more fully. When you read more books about ancient Egypt, you expand your understanding of that civilization.

The word also describes spreading outward. The universe is constantly expanding, with galaxies moving farther apart. A puddle expands across the sidewalk after rain. When a company expands its operations, it grows by doing more things or serving more customers.

Notice that things can expand in different ways: slowly and steadily like a growing tree, or quickly like popcorn kernels bursting in a hot pan. When something has room to grow or spread out, it has space to expand.