.dw directive in AVR assembler
I found the answer in the application note:

"The Z-register in the register file is used to access the program memory. This 16-bit
register pair is used as a 16-bit pointer to the program memory. The 15 most signifi-
cant bits select the word address in program memory. Because of this, the word
address is multiplied by 2 before it is put in the Z register."

Thanks to isdi for his comment