What is meant by the 8 stages of insight?
This is 7 purification and 16 stages of insight. See:


The Progress of Insight
Transcendental Dependent Arising
Relay Chariots
7 Stages of Purification &amp; The Insight Knowledges
A Map of the Journey (Very readable book)
The Development of Insight
The Sixteen Stages of Insight


NB: Don't get too engrossed in the stages. Many of the naturally manifest them self. You cannot force the development or crave for it to come. Either way you are regressing.