What is a subsidiary in business, as in "Company A is a subsidiary of company B"?

All that this means is that one company is owned and
controlled by the other company.  If Company A is a subsidiary of Company B, then
Company B holds the majority of the voting stock in Company A and can control Company
A's operations.  As an example of this in the US, the Time-Warner corporation has
subsidiaries such as CNN and HBO.

It is very common for
companies to have subsidiaries or to be the subsidiary of another company.  One major
reason for this is so that the parent company can have many sources of income without
becoming too centralized.  The parent company can benefit financially but can still
allow the subsidiaries to have their own management teams that are expert in their
particular area.  Such subsidiaries are also easier to sell if that becomes
appropriate.