Area 51 is a highly classified remote detachment in the United States Air Force. It's been a top secret place of the government, and no one is allowed to enter except officials. People have assumed that there is the existence of aliens and dangerous experiments are done in Area 51. Also, Many movies are built on this phenomenon making the people more curious about the area.
Social media was flooded with memes of Area 51 when a meme page on Facebook created an event, "Storm Area 51, they can't stop all of us". Further, it said if enough people attempted to access the highly secured US research facility. The government will not be able to prevent people from entering the area. And maybe they will discover the rumoured weapons or evidence of Aliens.
Since the event was created, about 250,000 people got interested in the event, and thousands agreed to participate in the event. For the record, the event was fake and made just for fun.
The Internet found it pleasantly entertaining and has made memes out of it; relating to how the military will block people and how people will react.