If you're asked if there are "obstructions" between your antenna or dish and another location, you might have sheepishly said no, not knowing what an obstruction is.
"Obstruction" is just a fancy word for something that comes between you and what you're trying to see. In the suburbs, the most common obstruction is a tree that blocks the path between your antenna and the broadcast towers, or between your dish and the sky.
The path between your antenna or dish and the thing it needs to see is called "line-of-sight," by the way, and if you have good line-of-sight it means that you can see what you need to see. Or, at least, your dish can... those satellites are awful small and hard to see with the naked eye at 22,000 miles away