Definition of retros:
(adj) :
Of, or relating to, the past, past times, or the way things were.
(n) :
(uncountable) Past fashions or trends.
(adj) :
Affecting things past; retroactive, ex post facto.
(n) :
(chess) A chess puzzle of retrograde analysis, requiring the solver to work out the history of moves leading to the position presented.
(n) :
(countable) Abbreviation of retrospective. [An exhibition of works from an extended period of an artist's activity.]
(n) :
(countable) Abbreviation of retrorocket. [A small rocket engine on a larger rocket or spacecraft, designed to slow or reverse its motion.]