What''s the difference between GL_CLAMP_TO_EDGE and GL_CLAMP?

Quoted from the Red Book (for OpenGL 1.2) :

- For the wrapping mode GL_CLAMP, the texel from the border (or GL_TEXTURE_BORDER_COLOR) is used in the 2x2 array of weighted texels.

- For the wrapping mode GL_CLAMP_TO_EDGE, the border is always ignored. Texels at or near the edge of the texture are used for texturing calculations, but not the border. (GL_CLAMP_TO_EDGE is new to OpenGL 1.2)