Authenticity is begin truly original not a copy of something or someone , completely genuine.
In this century it can be difficult to be truly authentic compared to the 20th century after world war one when in a modernist art movement when photography want considered an art form it was seen as an authentic way of seeing things but then these days its easy to say your a photographer with just taking a photo on your phone.
Its hard to be completely authentic in todays era as we are exposed to so much art that our own work can appeared as a copy even though we may have never seen the work that looks similar to our own. However it can be possible to be authentic in contemporary practice it just a lot harder as everyone seems to have an opinion .