The name of "Royal" is given because it has state rank and it is the King who is responsible for sanctioning and ordering the publication and compliance of the rule.
The Constitution says literally: In case of extraordinary and urgent need, the Government may issue temporary legislative provisions which shall take the form of decree-laws ...This means that there are two fundamental conditions to use the form of the Royal Decree-Law: that the measures must be implemented urgently (and cannot be carried out by the normal parliamentary process because it is very slow), and that the Decree-Law is created because of situation of extraordinary necessity.
The Constitution enumerates a series of subjects on which the Decree-Law does not have the capacity to legislate.
These are: The Decree-Law is temporary and, according to the Constitution: Decree-Laws must be immediately submitted for debate and voting by the entire Congress, which must be summoned for this purpose if not already in session, within thirty days of their promulgation.This means that within 30 days, the Congress must debate whether or not the Decree-Law is valid and has three possibilities: The Royal Decree-Law may occupy the "place" or regulate matters that would be dealt with by ordinary law, but never of those matters reserved for the organic law (fundamental rights, autonomy statutes, electoral regime, etc.).
If the Constitutional Court considers that the situation is not one of urgent and extraordinary need or that if the subject matter is not within its competence, it may declare it totally or partially unconstitutional and expel it from the legal system.