A chemical weapon is a special kind of weapon, like a bomb, that hurts or kills people by using chemicals. Instead of hurting people with their force, chemical weapons poison people. These kinds of weapons have been around for a long time, but most countries now agree that they are against the law.
In the past, many countries created lots of chemical weapons. Now 192 countries have agreed not to use chemical weapons and to get rid of the ones that they have.
(Source: US Government, via Wikimedia Commons.)
But some countries, such as Syria, have kept on using chemical weapons. Usually other countries protest when this happens.
When people talk about chemical weapons, they usually mean weapons that can kill people or make them very, very sick. But some chemical weapons are less strong. They can make it hard for people to work or fight, without hurting them badly or killing them.
Surprisingly, even though it is against the law to use chemical weapons in a war, they are sometimes used in other ways. Police may use chemical weapons like tear gas or pepper spray to stop groups of people who are protesting or attacking.