A complication is something that makes a situation more difficult or complex than it was before. When doctors perform surgery, they hope there will be no complications: unexpected problems like infections or bleeding that make recovery harder. When you're planning a camping trip and a thunderstorm rolls in, that's a complication that forces you to change your plans.

The word comes from the idea of things becoming “folded together” in a tangled way. Simple problems have straightforward solutions, but complications add new layers of difficulty. If you forget your homework, that's a problem. If you forget your homework and your teacher is collecting it for a grade and your parents are meeting with her that afternoon, those are complications that make the original problem much harder to solve.

Sometimes people say “it's complicated” when a situation has so many factors and complications that it's hard to explain quickly. A friendship might become complicated when two friends both want to be team captain, or when one moves away but wants to stay close.

In stories, complications are the obstacles that make the plot interesting. Without complications, the hero would simply walk up and solve the problem. The complications, the unexpected difficulties and setbacks, are what make the story worth telling.