Standalone Server
For many use cases, the centralized management capability available
via a managed domain is not necessary. For these use cases, a JBoss
Application Server 7 instance can be run as a "standalone server". A
standalone server instance is an independent process, much like an JBoss
Application Server 3, 4, 5, or 6 instance is. Standalone instances can
be launched via the standalone.sh or standalone.bat launch scripts.
If more than one standalone instance is launched and multi-server
management is desired, it is the user's responsibility to coordinate
management across the servers. For example, to deploy an application
across all of the standalone servers, the user would need to
individually deploy the application on each server.
It is perfectly possible to launch multiple standalone server
instances and have them form an HA cluster, just like it was possible
with JBoss Application Server 3, 4, 5 and 6.
Managed Domain
One of the primary new features of JBoss Application Server 7 is the
ability to manage multiple JBoss Application Server 7 instances from a
single control point. A collection of such servers is referred to as the
members of a "domain" with a single Domain Controller process acting as
the central management control point. All of the JBoss Application
Server 7 instances in the domain share a common management policy, with
the Domain Controller acting to ensure that each server is configured
according to that policy. Domains can span multiple physical (or
virtual) machines, with all JBoss Application Server 7 instances on a
given host under the control of a special Host Controller process. One
Host Controller instance is configured to act as the central Domain
Controller. The Host Controller on each host interacts with the Domain
Controller to control the lifecycle of the application server instances
running on its host and to assist the Domain Controller in managing
them.
Modo Standalone x Domain
O modo Standalone é o modo tradicional das versões anteriores. Basicamente implica em ter uma instalação diferente (ou um diretório standalone diferente) para cada instância1 de Wildfly. Ou seja, para cada Wildfly rodando no seu ambiente é necessário alterar seus próprios arquivo de configuração, suas próprias opções de execução para JVM, etc.
O modo Domain é o modo que foi introduzido no JBoss AS 7 onde é possível gerenciar um conjunto de instâncias Wildfly, agrupando-os e assim permitindo compartilhar configurações comuns entre eles. Além de compartilhar configurações, é possível também através de um único console de gerenciamento iniciar ou parar instâncias (ou grupos inteiros), verificar seu status e estatísticas de cada subsystem (falaremos sobre isso mais adiante), etc
Fonte :https://jboss-books.gitbooks.io/wildfly/content/estrutura/modo_standalone_x_domain.html