Db dw dd and DUP

DB defines a byte define byte (1 byte)
DW defines a word define word (2 bytes)
Dd defines a double-character define double word (4 bytes)

DUP is an operator. In assembly languages, DUP is the same as DB, DW, and DD. It is also a symbol recognized and processed by the compiler.
It is used with data definition pseudocommands such as DB, DW, and DD for data duplication.
For example
DB 3 DUP (0) is equivalent to db 0, 0
DB 3 DUP (, 2) is equivalent to DB, 2, 2, 2
DB 3 DUP ('abc', 'abc ')
The format is as follows:

DB repeat times DUP (repeated byte data)
DW repeated times DUP (repeated font data)
Dd repeated times DUP (repeated double-font data)