They are "absolute" ways of saying yes and no. They're also non-standard, so avoid them until you know it's perfectly OK.

It is a very casual way of saying "yes and no" , used in some regions.

yep and nope are very informal way to say ¨yes ¨and ¨no ¨ . Don't use them in a formal conversations.

yep: informal form of yes nop : informal /spoken form of no