Semayne's Case is a very old legal case that happened a long time ago, in the year 1603 in England. At that time, people didn't have many laws to protect their homes from the "bad guys," and there weren't that many police officers or lawyers around. So, when someone wanted to enter someone else's home, they could just go right in without asking.
But then, a man named George Semayne had enough of this kind of thing. He owned a house and he wanted to make sure that nobody could come inside without his permission. He went to the judges and asked them to help him. He told them that he wanted to make his home more safe and secure, and he didn't want anyone to come into his house unless they had a good reason.
The judges thought about it and they agreed with George. They said that people should have the right to protect their homes from strangers, even if those strangers were police officers or government officials. The judges said that "Semayne's Case" meant that people should have the right to privacy in their own homes, and that the police would need a really good reason to enter someone's home without their permission.
So, from that day forward, the police couldn't just burst into someone's house without a good reason. They had to have a warrant or some other legal document that gave them permission to enter. This helped make people's homes feel safer and more secure, and it's still an important law today.