Windows Server is the operating system that bridges on-premises environments with Azure services enabling hybrid scenarios and maximizing existing investments, including:
Your use of the Windows Server images from Azure Marketplace Virtual Machine Gallery are provided to you for use with virtual machine instances under your Azure subscription which are governed by the Online Services Terms. These virtual machine instances are limited for use with Azure.
Windows Server 2019 is the latest Long-Term Servicing Channel (LTSC) release with five years of mainstream support + five years of extended support. Choose the image that is right for your application needs: 1) Server with Desktop Experience includes all roles including the graphical user interface (GUI), 2) Server Core omits the GUI for a smaller OS footprint, or 3) Containers option include either Server with Desktop Experience or Server Core as the container host OS, with ready-made container images included (both Nano and Server Core containers).
Windows Server Semi-Annual Channel releases deliver new operating system capabilities at a faster pace and are based on the Server Core installation option of the Datacenter edition. A new release comes out every six months and is supported for 18 months. Check the Lifecycle Support Page for support dates and always use the latest release if possible.