viewer

/V Y UW1 ER0/
noun
  1. 1

    Someone who views a spectacle; an onlooker or spectator.

  2. 2

    Someone who watches television.

  3. 3

    Any optical device used to view photographic slides.

  4. 4

    A program that displays the contents of a file.

  5. 5

    The manager of a colliery, who directs its workings and ventilation.

Source: https://en.wiktionary.org/wiki/viewer