234C regarding

Under these section interest is levied on the amount being unpaid as advanced tax in the previous financial year
As there are 4 dates on which advance tax shall be paid which are as follows
15 june=15%of advance tax must be paid
15 September =45%of advanced tax must be paid
15 dec=75% of advance tax must be paid
15 March =100% of advance tax must be paid
If the assesse fails to pay the amt. as specified above on or before the due dates interest is levied on them under section 234C @ 1%per month
And time period for calculating interest is 3 months for June, September, December late paying and 1 month for March it's fixed, i.e. it doesn't depends upon on which date u paid the tax

In simple word u can say the interest which is levied for late payment of advance tax in the previous financial year

Thanks