IaaS gives you infrastructure (VMs, networks), PaaS gives you a managed runtime/platform (deploy code, provider runs it), and SaaS is a ready-to-use application (you just use it).
Advanced answer
Deep dive
These models describe **who manages which layers** of the stack.
**IaaS** (Infrastructure as a Service): you get compute/network/storage primitives (VMs, VPC, disks). You manage OS, runtime, deployments, scaling.
Examples: AWS EC2, GCE VMs, Azure VMs.
**PaaS** (Platform as a Service): you deploy an app/container; the provider manages runtime, scaling, patching, and often observability.
Examples: Heroku, Google App Engine, Azure App Service.
**SaaS** (Software as a Service): you consume a finished product; you configure it but don’t operate the platform.
Examples: Gmail, Slack, Salesforce.
Trade-offs
More control (IaaS) → more operational work.
More abstraction (PaaS/SaaS) → faster delivery but less flexibility.