A well-defined character is often considered a protagonist or dynamic person. Someone who can change for better or for worse, and hold onto their values with religious loyalty.
Good character example: Rosalind in Shakespeare's As You Like It. She is a true character who sticks to genuine and moralistic expectations of the society around her, while helping others advance their ideas of love.
Bad character example: Tom Buchannon from The Great Gatsby. He's rigid and a static character. His selfishness ultimately earns him a lack of trust in Nick and a torn marriage.