Aggregate of all 6 semesters of bachelor's degree.
As per rules of ICAI, bachelor's degree candidates in commerce stream with 55% marks or more in graduation can directly appear for IPCC stage. For non commerce stream, it is 60% marks.
Those who have less than required percentage have to appear for CPT !
upcoming to your question - Take total of all marks ontained in all semesters and divide it by overall total marks of semesters to arrive at aggregate percentage.