What does dw, db and ? (question mark) mean in TASM struc?

Question

I'm new to assembly, and now I'm trying to figure out what do the dw, db, and ? mean in a struc.

For example here:

struc segment_descriptor
  seg_length0_15        dw      ?
  base_addr0_15         dw      ?
  base_addr16_23        db      ?
  flags                 db      ?
  access                db      ?
  base_addr24_31        db      ?
ends segment_descriptor

Answer 1

"dw" is variable of type WORD, "db" is variable of type BYTE, dd is variable of type double word (int32_t). "?" means the values are not initialized.