Shell defines a thin wall solid.

Design > Solid > Modify > Shell 

Faces/Body

Enables the selection of the body to shell or faces to remove from the solid.

Tangent Chain

Specifies whether to include tangentially connected faces, or select individual faces to remove.

Inside Thickness

Specifies the wall thickness inside the solid.

Outside Thickness

Specifies the wall thickness outside the solid.

Direction

Select the direction for the wall thickness.

• Inside Offsets the faces toward the interior of the part.
• Outside Offsets the faces toward the exterior of the part.
• Both Offsets the faces toward the interior and the exterior of the part. You can have different values for the offsets.