In recent decades there has been a lot of drama and no short controversy surrounding this word...

Some Have been outright misinformation and hysteria fostered by Nollywood, the Wikipedia article on this topic not helping too.

In an attempt to deconstruct and demystify all these misconceptions...

Osu does not equate to an outcast (Onye ajuru ajuru) neither is it a caste system of social ranking or stratification as in the Hindu system.. Osu is a religious institution of the Traditional Igbo religion thus one cannot understand it without trying to understand the Traditional pre Christian worldview

Osu comes from the verb root i'su' meaning to offer, e.g isu aja, to offer sacrifice, osu means a devotee.

In the real sense an osu is a priest. The one who offers sacrifice to a particular deity(Arushi) over which he is in charge of.

The main Osu is the living vessel of the deity hence he himself is an offering... the Osu is a freeborn he is not a slave..

The term later became extended to shrine servants who were known as umu osu or nwa osu, these nwa osu became an institution that set some people apart who offer up themselves in service of a deity... these shrine servants being the property of the deity were a set apart class, they lived around the vicinity of the shrine or on any of the sacred lands belonging to the deity. They equally fed from the shrine proceeds.

They assisted the main priest and carried his sacred ritual items...the kept the shrine premises and did artworks..or artisanship.

As a result it was forbidden to harras an Osu and Osu could not be sold into slavery, to harm an osu would attract the penalty of the gods.

The downside of these benefits was that the umu osu could not marry from the free born community and could only marry themselves. They also could not inherit land through the normal system except lands they now purchase. These were no done as discrimination but with the understanding that as spirit people they were not allowed to have carnal relations with the laity....why this did not apply to the main priest or the Eze and Durus i do not know.

The Osu participated in normal village life just like everybody, they were not feared or ostracized, they bought from the same market (forget Nollywood exaggeration)

The motivation for becoming nwa osu varied Some people became Osu by freewill some were forcibly dedicated to the deities by conquering village groups to service their deities... some out of economic difficulties... during the era of Aro slave trade, many people to protect from raids and being sold off ran into the shrines and became osu willingly...so Aro contributed to the sporadic proliferation of Osu in Southern Igbo.

On the advent of Christianity when many people started going to church, even as most of the Osu themselves had converted and abandoned the old gods... a type of stigma arose which associated the Osu as people dedicated to demons or the old Agbara/Arushi...and now that they were no longer attached to shrines and with most of the shrines gone, they were reluctant to accord Freeborn previlages to Umu osu, which is what led to most of the discrimination that arose gradually in the 20s and has persisted till this day. This demonstrates that the nuances surrounding the institution of osu is not easy as black and white and why marriage laws has not been easily bent...

All the Eze can keep coming together and government and bishops and make enactments upon enactments but at the end of the day they are powerless to make any change. E.g the Eze in Imo State who self righteously came out to make the pronouncement that no more osu in his community and then an Osu came to marry his daughter and he refused which shows his hypocrisy.

most of these Eze with their tiny fragmented autonomous communities are illegitimate and they know it. they are vestiges of the British colonial warrant chiefs and they have no real authority whatsoever in any spiritual matter. they do not have the ancestral ofo nu ogu so they cannot effect any change.

On Osu names, many people have tried to explain away the meanings just to assuage their Christian consciences... but Osu names means what it means e.g Osuala means a devotee/offering to the Earth goddess, Osuigwe(a devotee/offering to Igwe) Osuagwu(to Agwu) Osuchukwu etc.

Bearers of these names are not usually the umuosu but rather the main priest(who is the living vessel himself) or any freeborn child. The Igbo used to have a naming ceremony done on the 3rd week(2nd week in Southern igbo) the reason is because when a child is born, Afa is consulted, the parents must have done all the necessary consultations to know the child's destiny, the reincarnated ancestor or deity before the child is named... Children who have been determined to be living vessels of these divinities (Ala, Igwe, Agwu, Njoku) are named after them e.g Osuala, Osuji, Osuagwu, etc. there is no way to sugar coat it...the names mean just that.

The Nwaosu institution was very much entrenched in Isuama culture, as well as surrounding areas such as Agbaja groups, Ohuhu, Owerri groups.. it was not practised in western Igbo culture nor the Cross River Igbos. Thus is not a feature in the culture in Abia State.

I'll end by saying that the controversies that surround the Osu system, the marriages laws and all is not something that will go away automatically it is something only time can heal...