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(nasm.info)Section 3.2.5

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3.2.5. `TIMES': Repeating Instructions or Data
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   The `TIMES' prefix causes the instruction to be assembled multiple
times. This is partly present as NASM's equivalent of the `DUP' syntax
supported by MASM-compatible assemblers, in that you can code

     zerobuf:        times 64 db 0

   or similar things; but `TIMES' is more versatile than that. The
argument to `TIMES' is not just a numeric constant, but a numeric
_expression_, so you can do things like

     buffer: db      'hello, world'
             times 64-$+buffer db ' '

   which will store exactly enough spaces to make the total length of
`buffer' up to 64. Finally, `TIMES' can be applied to ordinary
instructions, so you can code trivial unrolled loops in it:

             times 100 movsb

   Note that there is no effective difference between `times 100 resb 1'
and `resb 100', except that the latter will be assembled about 100
times faster due to the internal structure of the assembler.

   The operand to `TIMES', like that of `EQU' and those of `RESB' and
friends, is a critical expression (*Note Section 3.8::).

   Note also that `TIMES' can't be applied to macros: the reason for
this is that `TIMES' is processed after the macro phase, which allows
the argument to `TIMES' to contain expressions such as `64-$+buffer' as
above. To repeat more than one line of code, or a complex macro, use the
preprocessor `%rep' directive.