There are a lot of things that one can say about characterization. In the most basic definition of characterization is the way a character in a story is portrayed by the author. With that said, there are many different ways in which an author can build characterization.
1. An author can just simply describe the character - physical appearance, emtional qualities, personal traits, etc.
2. An author can also indirectly build a character by the actions and thought of other characters.
3. There can be even more indirect ways to build a character, by allowing the reader only to see the actions of the character in view, so that the reader form an independent opinion.
In a word, there are many different ways to portray a character and the various ways are called part of what is called, characterization.
An example of characterization can be seen in the novel 'The Mill on the Floss' by George Eliot. Characterization in general relates to the way characters are portrayed by an author. This can take many forms, direct characterization,indirect characterization and allusion to give but a few. In the case of Maggie, she is shown as being hot-headed, clever,quick-witted but warmly emotional. However, these character traits, as Maggie finds to her intense irritation and frustration, are not attributes valued in females in her time. Some people are even upset by her mop pf curls which could be seen as an outward sign of her 'unruly-ness.' Eliot uses her personal description of looks to add characterization. Her mixed up convictions about her gifts make her vulnerable to low self-esteem caused by others.
In general, characterization means to discover what the character is about, their persona. Readers do this in many ways. Readers look carefully at dialogue, both from the protagonist (the main character) and from the characters around him or her. What others say about or to the main character can be revealing of a characters personality and motivation. The reader can also characterize by looking at the character's physical appearance, their actions, and even their gestures (for example Maggie in "Everyday Use" always looks down). Readers also look for direct and indirect characterization. This is how the narrator describes them. The narrator may come right out and say, "Maggie was shy," which is direct characterization, or he/she may say, "Maggie look ran behind the tree and peeped out at Dee," which is indirect characterization.