It is a word that is used to make the second list
correspond to the first list made in a sentence.
You will know by looking at this example:
"Let's buy a CPU, a memory chip, and a
motherboard because on the magazine, the reduced prices are 35, 45, and 60 dollars respectively."
You can see that by putting the word Respectively,
the reader now knows that the CPU costs 35 dollars since the two are both introduced in the first slot of the list.