Article 5 is a key part of the North Atlantic Treaty, which is the agreement that created NATO, the North Atlantic Treaty Organization. In simple terms, Article 5 is like a promise among the member countries of NATO. It says that if one of the member countries is attacked, the other members will consider it an attack on all of them and will help defend the country that was attacked.

Here's a bit more detail to help you understand:

1. Collective Defense: Article 5 is all about collective defense. This means that the security of all NATO members is tied together. If one is in trouble, the others will step in to help.

2. Only Used Once: Article 5 has only been used once in NATO's history. This was after the terrorist attacks on the United States on September 11, 2001. After these attacks, NATO members agreed that this was an attack on all of them, and they supported the U.S. in various ways, including military operations in Afghanistan.

3. Not Automatic: Just because Article 5 is invoked, it doesn't mean that every NATO country has to send troops or go to war. Each country decides how it will help. This could be through military support, but it could also be through other means like financial aid, intelligence sharing, or logistical support.

4. Peace and Security: The main goal of Article 5 is to keep peace and security in the North Atlantic area. By promising to defend each other, NATO countries hope to prevent conflicts and protect each other from threats.

5. Not Just for Any Attack: Article 5 is specifically for armed attacks. It's not for things like cyber attacks or political disagreements. However, NATO has been discussing how to handle new kinds of threats, like cyber attacks, within the framework of collective defense.

In summary, Article 5 is a crucial part of NATO that ensures all member countries will come to the aid of any member that is attacked, making it a powerful deterrent against aggression. It's like a group of friends promising to stand up for each other if one of them gets into trouble.