want to know about fixed deposit ?

hey guys

I just want to know what is fixed deposit I have nill knowledge about the fixed deposit, coz I have save money for my kid and which is the best place,like banks or postoffice please suggest me with right knowledge.

First of all I am not very sure if the loan taken ANY fixed deposit is a secured loan.?

Secondly, I also want to know if, I take a loan against a fixed deposit and I am not able to repay it, at the maturity date, I shall have a liability towards bank.
As far as basic logic says, bank did not lend any money to me and what I have is a part of my deposit.Why should bank ask for more money from me then?

Any pointer links to Reserve bank of India with norms for these conditions shall be helpful.