Infrastructure as a service. e.g. AWS, DigitalOcean, GCP A step away from on-prem [[infrastructure]].
Platform as a service. e.g. Heroku, Google App Engine. Allows the user to manage your own app without having to maintain infrastructure.
Software as a service. e.g. Dropbox, WebEx, Gmail. Also known as cloud application services. Pretty much everything is hnadled by the provider.