The word "Khawarij" is a plural form of the word "Kharijah" in fusah (formal Arabic).
Although in spoken Arabic it is common to refer to a single person as "Kharijiy" and to many as "Khawarij" which is quite different than the correct morphological rules of the Arabic language.
To make everything simple, "Khawarij" linguistically means "a group that has come out or gone out".
Sheikh Nasir Al Sabi'i stated that Ibn Al Faris has referred to the term linguistically as having two meanings, one being to pass through a thing, and another to differ in colours.
So linguistically, that's what Khawarij is supposed to mean: "One who has gone out or coming out."
The question most important to understand the term logically when we use it, is to determine what exactly is meant by going out or coming out.
Having determined the linguistic meaning of khawarij, which neither Sunni, Shia or Ibadhi will argue over, we must next state the technical meaning of the word "Khawarij".