technologies beside scaling web applications in a distributed nature

Question

Hello,

I am interested in theory to scale web applications in a distributed nature, i.e. when there is some platform/stack can be extended by others applications running on different servers, etc.

I am researching this field and feels the lack of the right keywords :)

Interesting concepts found so far:

• opensocial
• through API aka web services, like shopify does (shopify it's a hosted ecommerce solution)
• semantic web not quite sure about this one

Am I on the right way or am I lost anything? :)

Thanks.