Flat characters do not develop in a story; they stay the same. In addition, they are usually not very complicated. Static characters are the same thing as flat characters.
A dynamic character is the opposite of a static or flat character. They do develop in the story.
A protagonist is usually your main character. They undergo some development in the story and lead the action.
An antagonist is the opposite of your protagonist. Oftentimes, they oppose the protagonist's actions or get in the way. They are often enemies.
Lastly, a foil is a character who generally contrasts with the protagonist to bring out certain characteristics of the protagonist, usually in order to help them develop.
Hope this helps.
