An obstruction is something that blocks a path, process, or goal. When a fallen tree creates an obstruction on a hiking trail, you have to climb over it or find another route. When a catcher in baseball commits obstruction by blocking home plate without the ball, they're illegally interfering with the runner's path.

The word applies to physical obstacles and non-physical ones. A toy left on the stairs is an obstruction that could cause someone to trip. But obstruction can also mean deliberately preventing something from happening: if someone practices obstruction of justice, they're interfering with a legal investigation by hiding evidence or lying to authorities.

In everyday situations, you might encounter obstructions constantly. A backpack blocking the aisle obstructs people trying to walk past. A student who talks constantly during class obstructs others from learning. Snow or leaves can cause an obstruction in a gutter, preventing water from draining properly.

Notice how obstruction suggests something that shouldn't be there. A door is meant to block a doorway, so it's not an obstruction. But a chair wedged against that door becomes an obstruction because it prevents the door from serving its purpose. The word carries a sense that someone or something is in the way, whether accidentally or intentionally, stopping normal activity from happening.