Those who use this word correctly use it as it applies to the hierarchy of positions in the Roman Catholic Church, and also as it applies to the hierarchy of angels.
As thus used, the word refers to a very special kind of ordered series. There are series such as the series of fractions. The series of fractions is said to be continuous.
In contrast, a hierarchical series is not continuous. The series of integers is discontinuous in the sense that there is no number between one and two, between two and three, between three and four, and so on.
The only status among the prelates that is both higher than a priest and lower than a bishop is that of monsignor. In other words, the hierarchical order of positions in the Roman Catholic church is like the order of the integers, with a small finite number, in which the status of the Pope is highest, with which this hierarchical series ends.
When the word "species" is used philosophically by Aristotle to name the substantial forms that inhere in a number of individuals, he tells us that the order of the species, or substantial forms, is like the order of the integers, with a small finite number, in which the status of the Pope is highest, with which this hierarchical series ends.
In the case of the angels, which are minds without bodies, the hierarchy, topmost of which is Lucifer, the highest seraphim, includes nine orders of angels -- seraphim, cherubim, thrones, principalities, powers and so on, down to the lowest order of angels, which are the guardian angels, an order just beneath the archangel, in each of the nine orders, the angels belonging to that order are arraigned hierarchically. To understand this order, one must remember that each angel is a species, not an individual belonging to a species, as you and I are individual members of the human species.
The word "species" is also used of the members of botanical or zoological taxonomy. In the biological sciences, the word is used in. this sense, and there are hundreds of thousand of species of plants and animals.
But in the philosophical sense of the word "species," there are at most five species of substance -- elementary inanimate substances, composite physical substance, and three species of inanimate substance -- vegetative sensitive and rational.
The human species is the highest because it is rational. Aristotle tell us that this is a discontinuous series like the series of the integer, not like the series of fractions between zero and one.