What is a Subscriber Access License (SAL)?

A Subscriber Access License (SAL) is one of the options for licensing Microsoft software under a subscription model.  A SAL is required for each unique USER or DEVICE accessing a Microsoft product.  A SAL is not a concurrent license and hence cannot be shared amongst multiple users or devices.  Multiple users can access through a single device, or multiple devices can be used by a single user, however you cannot aggregate concurrent users through a single device ? individual user SALS are required.  Non-concurrent users through a single device is allowed.