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

Flexible Vertex Format Flags
Direct3D Immediate Mode uses flag values to describe vertex formats used for DrawPrimitive-based rendering. The D3dtypes.h header file declares the following flags to explicitly describe a vertex format and provides helper macros that act as common combinations of such flags. For more information, see About Vertex Formats.

Flexible vertex format (FVF) flags
D3DFVF_DIFFUSE
Vertex format includes a diffuse color component.
D3DFVF_NORMAL
Vertex format includes a vertex normal vector. This flag cannot be used with the D3DFVF_XYZRHW flag.
D3DFVF_SPECULAR
Vertex format includes a specular color component.
D3DFVF_XYZ
Vertex format includes the position of an untransformed vertex. This flag cannot be used with the D3DFVF_XYZRHW flag. If you use this flag, you must also specify a vertex normal, a vertex color component (D3DFVF_DIFFUSE or D3DFVF_SPECULAR), or include at least one set of texture coordinates (D3DFVF_TEX1 through D3DFVF_TEX8).
D3DFVF_XYZRHW
Vertex format includes the position of a transformed vertex. This flag cannot be used with the D3DFVF_XYZ or D3DFVF_NORMAL flags. If you use this flag, you must also specify a vertex color component (D3DFVF_DIFFUSE or D3DFVF_SPECULAR) or include at least one set of texture coordinates (D3DFVF_TEX1 through D3DFVF_TEX8).
D3DFVF_XYZB1 through D3DFVF_XYZB5
Vertex format contains position data, and a corresponding number of weighting (beta) values to be used for multimatrix vertex blending operations. Currently, Direct3D can blend with up to three weighting values (and four blending matrices).
Texture-related FVF flags
D3DFVF_TEX0 through D3DFVF_TEX8
Number of texture coordinate sets for this vertex. The actual values for these flags are not sequential.
D3DFVF_TEXTUREFORMAT1 through D3DFVF_TEXTUREFORMAT4
Number of values that define a texture coordinate set. The D3DFVF_TEXTUREFORMAT1 indicates one-dimensional texture coordinates, D3DFVF_TEXTUREFORMAT2 indicates two-dimensional texture coordinates, and so on. These flags are rarely used alone; they are used with the D3DFVF_TEXCOORDSIZEn macros.
Helper macros
D3DFVF_LVERTEX
Vertex format is equivalent to the D3DLVERTEX vertex type.
D3DFVF_TLVERTEX
Vertex format is equivalent to the D3DTLVERTEX vertex type.
D3DFVF_VERTEX
Vertex format is equivalent to the D3DVERTEX vertex type.
Mask values
D3DFVF_POSITION_MASK
Mask for position bits.
D3DFVF_RESERVED0 and D3DFVF_RESERVED2
Mask values for reserved bits in the flexible vertex format. Do not use.
D3DFVF_RESERVED1,
This bit is reserved to indicate that the system should emulate D3DLVERTEX processing. If this flag is used, the D3DFVF_XYZ, D3DFVF_DIFFUSE, D3DFVF_SPECULAR, and D3DFVF_TEX1 flags must also be used. This equates to the effect of the D3DFVF_LVERTEX helper macro.
D3DFVF_TEXCOUNT_MASK
Mask value for texture flag bits.
Miscellaneous
D3DFVF_TEXCOUNT_SHIFT
The number of bits by which to shift an integer value that identifies the number of a texture coordinates for a vertex.