From BlenderWiki

This panel appears in the Editing Context panel group which is accessed using F9 or clicking button in the Buttons window.

[edit] MetaBall tools

This panel affects each Meta Object individually.

• Stiffness - How stiff the mesh frame is.
• Ball - Configures a sphere. Similar to Elipsoid but with no volume settings, for example dx, dy or dz.
• Tube - Configures a capsule, with a dx volume control.
• Plane - Configures a rectangle, with a dx and dy volume controls.
• Elipsoid - Configures a squashed sphere, with a dx, dy and dz volume controls.
• Cube - Configures a box, with a dx, dy and dz volume controls.
• Negative - The Meta Object has the inverse effect on other Meta Objects. In effect it pushes "into" other Meta Objects.
• Hide - Hides the mesh. This is similar to setting "Never" on the MetaBall panel.