Bitrix24 Cloud version is SaaS, it is rented by our users. It is deployed, hosted and maintained by Bitrix, Inc. (USA) and Bitrix24 Limited (Europe) in the Cloud. You can use your Bitrix24 account with a free subscription, or with a paid plan. Note that before using Bitrix24 Cloud account and all services provided inside your Bitrix24 instance, you will need to read and accept the Terms of Service (ToS).
Bitrix24 On-Premise (Self-Hosted) version is licensed on "per-user basis". If you need more users than your license key provides, you can purchase On-Premise Edition Upgrades. Bitrix24 On-Premise is fully customizable (color schemes, layout, menu items, header, footer, etc.) and provided with the full source code. It can be deployed and hosted by the end-user or by Bitrix Partners.