A series is a group of related things that come one after another in order. When you read a book series like The Chronicles of Narnia or Percy Jackson, each book continues the story but can often stand on its own. When you watch a television series, you follow characters through multiple episodes that build on each other.

The word appears in many contexts. In mathematics, a series is a sequence of numbers added together, like 1 + 2 + 3 + 4. In baseball, the World Series is a sequence of games played between two teams to determine the champion. Scientists might conduct a series of experiments, testing the same idea in different ways to make sure their results hold up.

What makes something a series is that the parts connect to each other in a meaningful pattern or sequence. Your school day involves a series of classes. A factory assembly line uses a series of steps to build a product. The key idea is that the parts relate to each other and follow a logical order.

You'll also hear people use in series to describe things arranged in a connected chain, like batteries linked in series to increase voltage.