If your company owns Windows Server 2012/2016 Standard or Datacenter with Software Assurance, you might be entitled to a discount of about 40% on some Azure VMs.
Azure Windows VMs include the Windows licenses as part of the cost. However, if you have SA on your Windows Server licenses, you can repurpose them in Azure by selecting the base compute-rate VMs (which are essentially Linux labeled). Information on the special pricing can be found here.
In order to take advantage of this special offer, you need to either create the Azure VM by selecting the Azure Marketplace image, or by migrating an existing Azure VM using Azure Site Recovery and PowerShell.
The licensing benefit allows you to run two Azure VMs with up to eight cores, or one Azure VM with up to 16 cores, at the base compute rate described above. If you are licensed for Windows Server Standard, you must stop using that license on-premises in order to take advantage of the offer. Windows Server Datacenter allows you to keep using the licenses on premises as well as in Azure. You can read more about the offer here or download the Azure Hybrid Use Benefit datasheet.