From BlenderWiki
Panels
The buttons in each Context are grouped into Panels. Each panel is the same size and can appear in most types of Windows. They can be moved around the Button Window by LMB 
clicking and dragging on their header.
I - Script context
II - Shading Lamp sub-context
III - Shading Material sub-context
IV - Shading Texture sub-context
V - Shading Radiosity sub-context
VI - Shading World sub-context
VII - Object Object sub-context
VIII - Object Physics sub-context
IX - Editing context
X - Scene Render sub-context
XI - Scene Anim sub-context
XII - Scene Sound sub-context
XIII - Transform Properties
XIV - MetaBalls
XV - Armatures
