A company who is buying more than 51 % share from another 
company is called holding company.
 A company who is selling 51% shares to another company is 
Called parent company.

if the company is interested to go into new venture and it 
starts a new company giving part of its shares to new 
company.this is known as spin-off.example A company running 
a shoe business which share capital is rs10000.it decides 
to open a shoe polish business know as B company and gives 
rs 4000 shares out of rs10000 to B company and maintains 
6000 for its self.here  A company is parent company and B 
company is child company.
holding company is company which holds atleast 51% of 
shares of other company.