WebObjects uses three prefixes:
NS stands for "NextStep", a slightly historical tag, but this contains foundation classes such as arrays (NSArray), etc.
EO for "EnterpriseObject", data modeling layer, which was actually around before WebObjects
WO for WebObjects which is the view and control layer built on Enterprise Objects
The naming convention for objects in WebObjects is that names are written in CamelCase (which is somewhat controversial since long names are less readable and it is somewhat ugly).
WebObjects Directory Layout
The way in which the various development-time and deployment-time files, and collections of files, are organized, follows a convention established in history.