Wallet or Purse?

What is the difference between a Wallet and a Purse? Both as far as I know perform the same function. They hold your paper money, coins, credit cards etc. But why the different names?

I know they come in different styles for men and women, but why the different names?

I was looking on the Filofax UK site and I was looking at their 'leather accessories' section and then I saw Malden... must have a look.

Even Filofax has fallen in to this trap though.. I quite liked the look of the this Malden 'purse' in black. I thought that would be quite smart and secure. I want something that only carries cards, money, coins and my passport. That looks big enough and secure enough?

However, if you go back a step to the front page and see that you can select on 'gender' click on male and look everything is a wallet. Click on female and it's a purse. 

So it looks like I might have to go against convention once again... man bag plus purse... it's a bit worrying isn't it!