what is a round character also what is a flat character

Answer 1

Round characters: the main characters; you know lots more details about each of them than about the flat (minor) characters.
http://fictionwriting.about.com/od/glossary/g/RoundCharacter.htm

Flat characters: the minor characters; almost like props or background
http://fictionwriting.about.com/od/glossary/g/flatcharacters.htm