"A round character is one who is multidimensional, revealing the complexity and contradictions that are so much a part of human nature. E.M. Forster, who first used the phrase in Aspects of the Novel, wrote that the true test of roundness is in a character’s ability to surprise in a convincing way. The round character stands in contrast to the flat character, a term also coined by Forster. Flat characters tend to be defined by a single trait. They usually remain unchanged."

This is a quote and is a great help to those who wants to write a story.
The flat character is very predictable, you know what they are going to do. They are often the good friend or the bad guy, they never change.
Then there is your round characters, more life like. They have inner whants and desires, needs and dreams. They're feelings take a stranger path and these are the characters that can most likely surprise the reader.

I am always here to help just ask me. blaugh