What is Edictum?

Legal Definition
In the Roman law. An edict; a mandate or ordinance. An ordinance or law, enacted by the emperor without the senate; belonging to the class of constitutiones principis. Inst. 1, 2, 6. An edict was a mere voluntary constitution of the emperor; differing from a rescript, in not being returned in the way of answer; and from a decree, in not baing given in judgment; and from both, in not being founded upon solicitation. Tayl. Civil Law, 233. A general order published by the praetor, on entering upon his office," containing the system of rules by which he would administer justice during the year of his office. Dig. 1, 2, 2, 10; Mackeld. Rom. Law, ยง 35. Tayl. Civil Law, 214. See Calvin.
See also
-- Black's Law Dictionary
Legal Definition
An edict.
-- Ballentine's Law Dictionary