PRETERITION IS THE OMISSION OF ONE, SOME, OR ALL OF THE COMPULSORY HEIRS
The preterition or omission of one, some, or all of the compulsory heirs in the direct line, whether living at the time of the execution of the will or born after the death of the testator, shall annul the institution of heir; but the devises and legacies shall be valid insofar as they are not inofficious. (Art. 854)
By annulment of "the institution of heir", what is the "institution of heir"?