Duress in English law means coercing or pressurizing someone to do something against their will by using threats or violence. It's like when someone bullies you into doing something.
For example, imagine you have a big, scary friend who tells you to give him your candy or he will hurt you. This is duress. Your friend is using threats or violence to make you do something you don't want to do.
In English law, duress can be used as a defense in some cases. For example, if someone commits a crime because they were under duress, they may be able to argue that they were forced to do it and it wasn't really their fault.
However, not all forms of duress are accepted as defense. The threat must be serious enough to make a reasonable person fear for their safety or the safety of their loved ones. Additionally, if someone voluntarily puts themselves in a situation where they are likely to be placed under duress, they may not be able to claim duress as a defense.
In any case, it's important to remember that threats and violence are never okay, and it's always best to seek help if someone is bullying or threatening you.