I suppose it's talking about degrees. C:

Hi Steve and Phil, Thank you for your explanation about 80s, both of you are right as it should express the plurality of 80 to 89. Thank you all for reminding me! That helps me a lot!

The "s" means plural, a range of years — not just 80°, but 81°, 82°, all the way to 89°. The same goes for years: the 80s means 1980 - 1989.

No, "s" is NOT Fahrenheit degrees. :) "s" is used here to indicate plurality. Between the numbers 79 and 90 there are ten numbers. Those numbers are the numbers 80 through to 89, inclusive. Those ten numbers are "the 80s". "The 80s" can refer to the years 1980 to 1989 (inclusive) or to the range of temperatures in the range 80 to 89 (but you would have to separately specify what temperature scale you're referring to, since you can't tell from "the 80s". You'd have to say "the 80s Fahrenheit", or whatever) or to a person's age range, or other things.