Vacatio Legal is a legal term, of Latin origin, which means vacancy of the law, that is, "the Vague Law", which is the period that elapses between the day of publication of a law and the day it enters into force, that is, it is mandatory.
THE Vacatio Legal, legally based, is established so that there is a period of assimilation of the new law that will enter into force after the specified period. This period is an average of 45 days, counting from the date of publication of the law.
It is also possible that the new law waives the Vacatio Legis and thus must contain the following article: "This law shall enter into force on the date of its publication".
THE Indirect Vacatio Legis is the one that determines a new deadline for your period of Vacatio Legis, so that certain devices can be applied.
A law is in effect until a new law arises, and it may even be that the new law will discipline a fact for the first time. It is in this context that the moment when the new law starts to come into force is inserted, as well as to appreciate the reach of its effects on the acts practiced up to that moment.
Since the time of the Romans, the principle of non-retroactivity of the law has been in force, that is, no law could have its effects applied to facts and acts that have already taken place. It was at the beginning of the 19th century that liberal ideas sought to safeguard the so-called acquired right.