A quick definition of ex turpi causa:

Ex turpi causa: A Latin phrase that means "from an immoral consideration." It expresses the idea that a person cannot enforce an agreement that is based on something that goes against what is good for society. For example, if someone makes a deal to sell drugs, they cannot go to court to make the other person pay them because the agreement is illegal and harmful to society. This principle is important because it helps to protect the public interest and prevent people from benefiting from bad actions.