What is the difference between Distribution group and Dynamic Distribution group?

Mail-enabled (Universal distribution group): This is an Active Directory distribution group object that can be used only to distribute messages to a group of recipients.

Mail-enabled (Universal security group):A mail-enabled Active Directory security group object that can be used to grant access permissions to resources in Active Directory, and can also be used to distribute messages.

Mail-enabled (Non-universal group): This is an Active Directory global or local group object. Mail-enabled non-universal groups are de-emphasized in Exchange 2007 and can exist only if they were migrated from previous versions of Exchange. You cannot use Exchange 2007 to create new non-universal distribution groups.

Dynamic distribution group: A distribution group that uses recipient filters and conditions to derive its membership at the time messages are sent.