Nick is the main character in Andrew Clements' book entitled, Frindle, a story about the mayhem that ensues when fifth-grade Nick Allen decides to create a new word for a "pen." Mrs. Granger is Nick's English (language arts) teacher, and Nick is a very bright youngster.
If you asked the kids and the teachers at Lincoln Elementary School to make three lists—all the really bad kids, all the really smart kids, and all the really good kids—Nick Allen would not be on any of them. Nick deserved a list all his own, and everyone knew it.
Was Nick a trouble maker? Hard to say. One thing's for sure: Nick Allen had plenty of ideas, and he knew what to do with them.
With this in mind, Nick decides to challenge the particularly strict Mrs. Granger. Nick is something of a trickster, and likes to do all he can to distract his teacher and waste class time, but Mrs. Granger does not fall into these "traps." Something serious comes out of their "discussions" when Nick asks who decides what words go into a dictionary. Mrs. Granger tells him that he—and other people—decide, by using words.
Nick decides to call a pen a "frindle"—a word he makes up. For him, it starts out as a game, and from that point on, he refuses to use any other word for the writing implement than "frindle." Needless to say, it catches on and creates quite a stir not only in the classroom and in the school, but also in the town; it even makes it onto the news.
Though Mrs. Granger seems very strict, she is actually very interested in helping her youngsters grow, not only as students but as people. Nick and Mrs. Granger actually end up having more in common than they might have suspected at first—or perhaps Mrs. Granger had an idea, while it took Nick a while longer to catch on.
"Nick" is a nickname for "Nicholas," which is Nick's given name. The author specifies in the book's first sentence that "Nick" is the name that everyone uses to refer to him.