AWS provides Infrastructure as a Service or IaaS and ‘elastic computing resources’.  AWS is actually several ‘clouds’ regionally-based, named as Data Centers and within these, zones of availability.  Firms can avail themselves of these data centers and zones, with their associated server resources, through a set of APIs or application programming interfaces.  AWS’ main innovation is to present to their clients a coherent and easy-to-use API access to complex server, hardware, compute, network, and storage services. 

Presentation is attached, which helps summarize the key concepts and Design Principles, around building a reliable system and platform in AWS.