Brahmacarya, gārhasthya, vānaprastha and sanyāsa are the four āśramas we find in the tradition. Among these, the fourth one is the most important because it deals with mōkṣa(a state where there is no sorrow or rebirth). In tradition, we find six types of it. We have an extensive detail in the 108 upanishads with commentary by upanishad brahmendra.