Enterprise Architecture is a term initially coined within the context of addressing problems of system integration. To share information and support business processes from end to end it is typical to integrate systems together. Some years ago Manufacturing Resource Planning susye,ms were connected to accounting systems and ERP resulted, for example. There is still a strong need to connect systems together, via SOA, EAI, ESB or other means.
When you take items vended as a system, like ERP, and connect them to other systems you get a system of systems.
"If you do anything long enough, you eventually get good at it." MK