Major or central characters are vital to the development and resolution of the conflict. In other words, the plot and resolution of conflict revolves around these characters.
Minor characters serve to complement the major characters and help move the plot events forward.
Dynamic - A dynamic character is a person who changes over time, usually as a result of resolving a central conflict or facing a major crisis. Most dynamic characters tend to be central rather than peripheral characters, because resolving the conflict is the major role of central characters.
Static - A static character is someone who does not change over time; his or her personality does not transform or evolve.
Round - A rounded character is anyone who has a complex personality; he or she is often portrayed as a conflicted and contradictory person.
Flat - A flat character is the opposite of a round character. This literary personality is notable for one kind of personality trait or characteristic.
Stock - Stock characters are those types of characters who have become conventional or stereotypical through repeated use in particular types of stories. Stock characters are instantly recognizable to readers or audience members (e.g. the femme fatale, the cynical but moral private eye, the mad scientist, the geeky boy with glasses, and the faithful sidekick). Stock characters are normally one-dimensional flat characters, but sometimes stock personalities are deeply conflicted, rounded characters (e.g. the "Hamlet" type).
Protagonist - The protagonist is the central person in a story, and is often referred to as the story's main character. He or she (or they) is faced with a conflict that must be resolved. The protagonist may not always be admirable (e.g. an anti-hero); nevertheless s/he must command involvement on the part of the reader, or better yet, empathy.
Antagonist - The antagonist is the character(s) (or situation) that represents the opposition against which the protagonist must contend. In other words, the antagonist is an obstacle that the protagonist must overcome.
Anti-Hero - A major character, usually the protagonist, who lacks conventional nobility of mind, and who struggles for values not deemed universally admirable. Duddy, in Mordecai Richler's The Apprenticeship of Duddy Kravitz, is a classic anti-hero. He's vulgar, manipulative and self-centered. Nevertheless, Duddy is the center of the story, and we are drawn to the challenges he must overcome and the goals he seeks to achieve.
Foil - A foil is any character (usually the antagonist or an important supporting character) whose personal qualities contrast with another character (usually the protagonist). By providing this contrast, we get to know more about the other character.
Symbolic - A symbolic character is any major or minor character whose very existence represents some major idea or aspect of society. For example, in Lord of the Flies, Piggy is a symbol of both the rationality and physical weakness of modern civilization; Jack, on the other hand, symbolizes the violent tendencies (the Id) that William Golding believes is within human nature.