SAAS or Software as a service

So whats software as a service all about

Its when you pay the software fee as a subscription like monthly fee.

Most providers will provide upgrades to you that are included in your subscription.

Sometimes the software is hosted by the provider and you don't have to manage infrastructure to host and deploy it.

There is Co-location services and Platform as a service too where you don't have to implement infrastructure but just lease it from another provider and they manage your infrastructure at the root level. Network, Building, backups, backup power and other infrastructure needs are handled by the provider of these services.

As far as applications you manage the server and applications on them.