Martial law is the system of rules that takes effect when the military takes control of the normal administration of justice.
Usually martial law reduces some of the personal rights ordinarily held by the citizen, limits the length of the trial processes, and prescribes more severe penalties than ordinary law. Under martial law the death penalty, death of personality, and even spacing can be administered to crimes that under normal law would not receive such harsh punishment.
In many countries martial law imposes particular rules, one of which is curfew. Often, under this system, the administration of justice is left to a military tribunal, called a court-martial. The suspension of the writ of habeas corpus is likely to occur.
Martial law is sometimes imposed during wars or occupations in the absence of any other civil government. Martial law can also be enacted during times of domestic strife, to protect against outside influence.
Earth Alliance President Morgan Clark enacted martial law in 2260, in response to the destruction of a Shadow vessel that had attacked Ganymede, though the attack was blamed on the White Star.  The fashion in which Clark did so was blatantly unconstitutional, but Clark-loyalists were by this point so integrated into both Earthforce and civilian authorities that it was impossible to challenge him.