It is
traditional in most societies that when a
couple gets
married, that they are presented with
gifts.
The problem with gifts is that people tend to be unimaginative in their selection. This means, that, for example, you are likely to get 4 toasters, 3 knife sets, 16 fruit bowls and none of the things you really want, like his and hers light sabres (true story: a couple of distant friends included light sabres on their bridal registry).
The bridal registry is a solution to this problem that has been adopted by many couples in Western countries. Basically it works like this:
The bride and groom visit a department store and pick out a list of all the gifts they'd like.
On the wedding invitation you include information about where the bridal registry is kept.
Guests to the wedding look at the bridal registry and choose a gift for you.
There are also some cons to bridal registries. Firstly, they're a little bit crass and make the couple look and feel guilty. Secondly, it discourages creative gift selection. Thirdly, they "lock you in" to one particular chain of department stores.