data input [D(n)(x)]

Those inputs whose states represent the data that is to be written into the selected address on a write cycle of an alterable memory device. When the numbering of the data inputs is significant for device operation, the data inputs are numbered beginning with 0. In devices where data bit groupings have independent control, an additional suffix "x" is applied. "x" takes the values of a, b, c, etc.

References: 

JESD21-C, 1/97