NGO is as everyone said, "Non Governmental Organization."

This would include groups like WHO, the Red Cross, The Knights of Columbus - groups that give AID of some kind without direct backing of a government. Often the aid is direct - tsunami relief, e.g. Sometimes it's meant to help establish infrastructure - like schools or hospitals or election monitoring.

I'm not sure if there's any variaton in the interpretation of the term. I read it in the news and in reports internal to the company where I work. I only became aware of the abbreviation in the last year or two, but it's probably been around a lot longer and I only just became aware of it.

The acronym /not-acronym question is interesting. The way these things are used sometimes by the "in crowd" can be a little confusing to the spectator - at least to this spectator. It sounds a lot like "Engio." Some abbreviations just sort of naturally lend themselves to this kind of thing. They just sound like words.