We typically provide Software as a Service (SaaS) to our customers, which includes the following layers.
Networking - Internet Connection & Bandwidth w/ Disaster Recovery
Storage - Cloud Storage
Servers - Cloud Processing
Virtualisation - Elastic expansion of storage, processing and bandwidth
Operating System - Linux Operating System with MySql Database
Middleware - Software to connect the data and application layer
Runtime - 30+ technologies to ensure speed and scalability
Base Applications - Application to solve a business problem (like CRM)
Customer Customisations - Custom code to suit the specific business process of a customer.
Customers typically only interface with the mobile apps and web applications.
for more information on PaaS vs SaaS