poorasian

What is your favorite complexity class and why is it F-Hard?

It came from the optimization literature. https://books.google.com/books?id=gtoTkL7heS0C&pg=PA283&lpg=PA283&dq=F+Hard+complexity+class+optimization&source=bl&ots=ZzY70UWKrj&sig=L12TIwyYnkdg31oKVqtAoY-vMwM&hl=en&sa=X&ved=0ahUKEwiO3MbHmcXTAhVP9WMKHYE8ANcQ6AEIVDAI#v=onepage&q=F%20Hard%20complexity%20class%20optimization&f=false

What would be the right name to call it? I'm not really from that field of math.