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.
I have three fruits: A banana, a bundle of
grapes, and some oranges, and respectively, they are
yellow,
purple and orange.