A roadblock is a barrier placed across a road to stop vehicles from passing. Police might set up a roadblock to check for dangerous drivers or to prevent someone from escaping after a crime. Construction crews use roadblocks to keep cars away from dangerous work zones.

The word also means any obstacle that prevents progress toward a goal. When you're working on a school project and realize you need information from a book that's checked out of the library, that's a roadblock. When a scientist's experiment keeps failing because one piece of equipment isn't working, that equipment becomes a roadblock to her research.

Some roadblocks can be removed or worked around. If the library book is unavailable, you might find the same information online or in a different book. Other roadblocks are more serious and might force you to change your entire approach. A team building a treehouse might hit a roadblock when they discover the tree isn't strong enough, requiring them to pick a different tree entirely.

When people say they've “hit a roadblock,” they mean something has stopped their forward motion, at least temporarily. The key is figuring out whether you can remove the roadblock, find a way around it, or take a completely different path.