Habeus corpus is Latin. It means "you have/or should have the body."
Basically, the government has limited authority to hold or imprison someone. They can't put you in jail for more than a day or two unless they have a court order. (Order = a judges decision, usually written).
if the government (or an agency of government, like the police) hold you for more than a day or two, without a court's permission, someone can bring a petition of habeus corpus in court for your benefit, against the government, demanding that the government explain why they've detained you. If the court doesn't agree with the government, the court orders your immediate release.
To "strike" something from an order means to "remove" it.