A more thorough explanation:

A duel is a prearranged combat between two or more people using deadly weapons. It is usually fought to resolve a previous quarrel or to avenge a deed. The combat is conducted under prescribed rules and in the presence of at least two witnesses.

In the past, duels were considered legal in some countries. However, in England and the United States, death resulting from a duel is treated as murder. Seconds, who are the people who assist the duelists, may also be liable as accessories.

Here is an example to illustrate the definition:

John and Peter had a disagreement over a business deal. They decided to settle their dispute through a duel. They agreed to use pistols and to fight at dawn the next day. The duel was witnessed by two of their friends. Unfortunately, John was shot and killed during the duel. Peter was charged with murder and his second was charged as an accessory.

It is important to note that dueling is illegal in most countries today. It is a dangerous and violent way to resolve conflicts. It is better to seek peaceful and legal means to settle disputes.