Text and description quoted verbatim from Microsoft DirectX 7 help file, included here for convenient reference.

The D3DFILLMODE enumerated type contains constants describing the fill mode. These values are used by the D3DRENDERSTATE_FILLMODE render state in the D3DRENDERSTATETYPE enumerated type.

typedef enum _D3DFILLMODE {
D3DFILL_POINT = 1,
D3DFILL_WIREFRAME = 2,
D3DFILL_SOLID = 3
D3DFILL_FORCE_DWORD = 0x7fffffff,
} D3DFILLMODE;

D3DFILL_POINT
Fill points.
D3DFILL_WIREFRAME
Fill wireframes. This fill mode currently does not work for clipped primitives when you are using the DrawPrimitive methods.
D3DFILL_SOLID
Fill solids.
D3DFILL_FORCE_DWORD
Forces this enumeration to compile to 32 bits in size. This value is not used.