Question: what is it called when a short story begins in the middle of a sequence of events?
Answer: A narrative work beginning in medias res (Classical Latin: [ɪn ˈmɛdɪ. aːs ˈreːs], lit. "into the middle of things") opens in the midst of the plot (cf. ab ovo, ab initio). Often, exposition is bypassed and filled in gradually, through dialogue, flashbacks or description of past events.