shadow-box

/SH AE1 D OW0 B AA0 K S/
noun
  1. 1

    A diorama

verb
  1. 1

    To practice moves without an actual opponent, often in front of a mirror.

    โ€œHe was shadow-boxing to keep fit and practice before the big fight.โ€

Source: https://en.wiktionary.org/wiki/shadow-box