Habeas corpus
that you have the body
Where the phrase comes from
The writ that orders a custodian to bring a person into court and justify the detention. In the United States, Article I, section 9 of the Constitution protects the privilege, with a narrow suspension clause.
What lawyers are pointing at
Habeas corpus tests the lawfulness of holding a person. It is not a verdict of innocence, and it is not a second criminal appeal under another name. The court asks why this body is in this custody. If the custodian has no lawful reason, the custody has to end. The phrase is a procedure. It is not a slogan for any complaint about a decision you dislike.
The same shape in code
A status page that says 'up' without a pid, a start time, and a live socket is a claim without a body. The operational cousin of the writ is: produce the process. If you cannot, the claim that the service is running has not been justified.
A concrete picture
A jail says a person is held on a warrant. The writ requires the warrant, or some other lawful basis, to be shown. A press release is not the basis.