What is "pish posh"

interj. nonsense; tommyrot.

Pish Posh is a children's novel by American author Ellen Potter, first published in 2006. It tells the story of a young girl, Clara Frankofile, who is a pompous, snobbish 11-year-old who spends her evenings people-watching from a corner table in her parents' chic New York City restaurant, Pish Posh.