Promenade concerts became extremely popular since the 18th century, they were announced as a new turn amidst the general public being accustomed to the traditional classic music performed predominantly in Albert hall or at times in Cardogan hall.
So, the promenade concert is a kind of outdoor concert where the public feel free to walk around the stage and even drink and eat during the performance. It was so unusual in those days that many people bought tickets to these concerts just of curiosity.
People who purchased full-season tickets were named "prommers", though in a while this term had been reffered to all visitors of the promenade concerts. But the main idea of the promenade concerts has stayed the same till nowadays, - to get a pleasure from classical or orchestral music performed by renowned virtuosos.