It is a cloud platform provided by Microsoft where you can manage your documents and e-mails anywhere and anytime. For detailed information: 

There are 2 types of SQL licensing:

Core Based Licensing: Licensing based on per physical core. It differentiates from physical and virtual SQL Servers. There is no user limit for server access in despite of Server + CAL licensing model.

Server + CAL Licensing: It is a model allowing you to license of SQL Server software per server and user. Client Access License (CAL) is a licensing model when users or devices use in order to access SQL Server. CAL licensing separates into Device CAL and User CAL.

It is an agreement allowing you to obtain legal tenure for computers without license. It cannot be moved to another computer. It has to be used with the computer assigned very firstly. 

It is a license given to computer producers in order them to install into the new computers. OEM license belongs to the computer in which it is installed. The license must be taken every time when a computer is bought. Also, it cannot be transferred to another computer. The life span of the license is the same with the span of the computer.  

It is suitable for companies having 2 or more machines to be licensed. It can be done at the minimum of 5 licenses. Open License is unique to the firm and it can be installed to another machine that is belong to the firm. When it is bought, the firm has a right to use lower version of the license.

Windows Server 2016 and 2019: Per-Core licensing. Microsoft has transformed its physical licensing into core-based licensing due to reason that producers increasing core amount in a single socket rather than processor amount. Windows Server 1 licenses only 2 physical cores in a single server. You can get 8 licenses at most. All active cores must be licensed in the physical server.