Floating licenses allow your customers to use a license on a limited number of machines simultaneously. For example, they can have your software installed on 100 computers, but only be able to use it on 20 of them at once.
This is similar to node-locked licenses (aka machine code locking) that is part of the Cryptolens for quite some time, with the exception that a license does not have to be deactivated when they are to be used on a new device.
Note: floating licenses are supported since v405 of Cryptolens.Licensing library for .NET. Support for C++ is coming soon.