what are we actually talking about when we are saying DECENTRALIZATION

A simple note for helping understanding decentralization in cyptocurrency world:

• what
  Decentralization means there's no such a centralized authority/org, like bank, to manage your account, including balance, transactions, and credential.
  Every single personal has to take full responsibility to his/her account.

• why it is important
  Nobody, even not for government, can steal your money unless you give him/her your password/key;
  Nobody managing your account also leads to a better privacy;
  Government can no longer rob your money by simply increasing the supply of paper money (fiat);
  Eliminating the middle man means lower cost during daily transactions, as you don't have to pay extra fee to middleman. (Usually there will be fees for transactions, but totally will cost you less than tradition one).

• how
  i'm not ganna go technical implementation, but will try to explain with human language. :)
  Say Todd wants to buy a toy from Alice using cyptocurrency, and they do the trade. At the moment they finished the trade, Todd's account should minus the price of the toy, and Alice's account will add the amount of cyptocurrency.
  As there's no such a bank who can help record this transaction (account balance changes), we need people around the Todd and Alice, say at least 7, to help confirm the transaction, like witness. Then all people over the world will agree the balance changes for account of Todd as well as Alice.
  This is basically how people will consent everyone's account balance. The cyptocurrency will run as simple as above illustration.
  You might be wondering what if others, like there're 8 people, deny the transaction before all other people get the confirm. Yes that will be an issue. Those kind of issues can be mitigated by technical solution and human intrinsic spirit (which is egotistic).