Different types of domains ?

I've just started to get in domain buying and would like to get to know a few things.What do all the domains mean?
1)Expired
2)Deleted
3) Dropped
4)TLD's

Thanks

i would like to know as well

Anybody here who'd care to enlighten me ?

1)Expired - If you own a domain and if you donot renew it, then the domain will get expired. You can renew your domain when it is in expired stage.
2)Deleted - The domains after the expired date will be deleted.
3) Dropped - It is the one which is available for re-registration.
4)TLD's - It is considered as the highest level domain for which all the low level domains will have this domain as the suffix.