Rectification

Self Asst means that When You Prepare Your Tax Return for Filing, You Calculate Your Income & Tax on the same based on the Income Tax Provisions (ie Your Way of Assessing your Taxable Income & Tax Liability Thereon) & You Pay that Tax.

Regualar Asst Means When Your Return Reaches the IT Deptthey scrutinise your Return & Details there on Check all the Heads on Incomes & deductions as Claimed by you & Calculate the Tax Liability there on & also check any TDS claim made by you if any if that matchs their record or no, & based on this details & their they do their workings ( In IT Language it is called as Asst) Since its done by the Dept themselves its named as Regular asst as it is done in their Regular course.

I hope now your concept of the Query is clear