The Maginot Line was a line of defense created by the French to ward off German invasion. It could house many French soldiers and was believed to be impenetrable. It was because of the Maginot Line that the Germans invaded Belgium and go around the line and invade France and so the line was a failure because of what the Germans did to defeat the French by June 1940.
the Maginot Line was a wall of concrete fortifications built by the French on their eastern border before World War II to defend against invasion by Germany. It failed because it wasn't mobile and the Germans pretty much just went around the concrete and cannon (which were fixed in place).
In general terms, it was a line of fixed fortifications, dug into the ground, consisting of artillery, etc. There were tunnerls connecting these fortifications, etc. The thought being the next war after WWI would be fought the same way WWI was fought. And it wasn't. The Germans essentially went around these fortifications, through the 'low countries' (Belgium, Holland and Luxembourg) when they invaded France in 1940.