In a story, what are major and minor characters?
The major characters are central to the story, narrative and plot, the minor characters are not.
We can see this by looking at some of Dickens' novels whichare good examples. In Nicholas Nickleby the eponymous character is obviously central to the story. Other major characters would include his villainous uncle Rafe, Rafe's illegitimate son Smike, and the brutal headmaster of Dotheboys Hall, Wackford Squeers. They are central to the story in their respective roles and also appear regularly, especially the first three.
Minor characters occur infrequently and have only a temporary and peripheral role in the story. These would include the miser Arthur Gride, his housekeeper Peg Sliderskew and the spendthrift Mr Mantalini.