Named User licenses (NUL)
"Named User Licenses are user-based licences, i.e. the license is bound individually to one person and not to a device. Users can therefore log in using their ID on different devices and use the software. Named User Licenses are applicable for the bring-your-own-device- scenario, i.e for instituitons that allow using computer owned by the organisation and private computers. Named User Licenses are abbreviated as NUL." 
NUL can be used up to 99 days offline and can be used on two devices if the devices are not used at the same time.
For more information see: