Definition of "retro"

retro

/ˈɹɛ.tɹoʊ/

adjective
comparative more retro, superlative most retro
1. Of, or relating to, the past, past times, or the way things were.
  Quotations
  Scientists say that while the public may think of the moon as a problem solved and a bit retro – the place astronauts visited a half-dozen times way back before Watergate and then abandoned with a giant "meh" from mankind – in fact, lunar studies is a vibrant enterprise that is yielding a wealth of surprises.
  2014 September 7, Natalie Angier, “The Moon comes around again ”, in The New York Times‎
2. Affecting things past; retroactive, ex post facto.
noun
countable and uncountable, plural retros or retroes
1. (uncountable) Past fashions or trends.
2. (countable) Abbreviation of retrorocket.
3. (countable) Abbreviation of retrospective.
  Quotations
  Richard Leacock's 1981 film portrait, Louise Brooks, was shown during a retro of Ms. Brooks's films at the Walker Art Center.
  1983, Sightlines, volumes 16-17, page 44