Object Coordinates are transformed by the ModelView matrix to produce Eye Coordinates.
Eye Coordinates are transformed by the Projection matrix to produce Clip Coordinates.
Clip Coordinate X, Y, and Z are divided by Clip Coordinate W to produce Normalized Device Coordinates.
Normalized Device Coordinates are scaled and translated by the viewport parameters to produce Window Coordinates.
Object coordinates are the raw coordinates you submit to OpenGL with a call to glVertex*() or glVertexPointer(). They represent the coordinates of your object or other geometry you want to render.
Many programmers use a World Coordinate system. Objects are often modeled in one coordinate system, then scaled, translated, and rotated into the world you're constructing. World Coordinates result from transforming Object Coordinates by the modelling transforms stored in the ModelView matrix. However, OpenGL has no concept of World Coordinates. World Coordinates are purely an application construct.
Eye Coordinates result from transforming Object Coordinates by the ModelView matrix. The ModelView matrix contains both modelling and viewing transformations that place the viewer at the origin with the view direction aligned with the negative Z axis.
Clip Coordinates result from transforming Eye Coordinates by the Projection matrix. Clip Coordinate space ranges from -Wc to Wc in all three axes, where Wc is the Clip Coordinate W value. OpenGL clips all coordinates outside this range.
Perspective division performed on the Clip Coordinates produces Normalized Device Coordinates, ranging from -1 to 1 in all three axes.
Window Coordinates result from scaling and translating Normalized Device Coordinates by the viewport. The parameters to glViewport() and glDepthRange() control this transformation. With the viewport, you can map the Normalized Device Coordinate cube to any location in your window and depth buffer.