What does Linux AHB, Windows AHB and SQL AHB mean?

AHB stands for Azure Hybrid Benefit. It is a licensing benefit that significantly helps to reduce the cost of running workloads in the cloud. 

For every VM (Windows, Linux or SQL) license you own with Software assurance. It is where you can start Azure for less by enabling AHB. 

Instead of using the basic "compute & infrastructure" and "software licenses" then pay for it in every VM. 

With Azure Hybrid Benefit enabled the on-premises window service license covers the cost of another two VM in Azure.