CST - Central Sales Tax. Applicable in case of inter-state sale. CST is applicable at rate of 2% or 1% against Form C (Registered Dealers), Form D (Individuals). In case of no Form C, CST is applicable at seller state's VAT rate.
VAT - Value Added Tax, Applicable in case of intra-state sale.
Technically when FK sells a item from Mum to Blr without Form C, CST has to be applied at rate of VAT. But many times seller charge VAT so that they save the work to file return / deposit tax in other head (VAT & CST).
A seller from Mumbai can never deposit VAT or CST in Bangalore. He has to file return from the place of issue of TIN#, CST#.