ArcGIS Pro offers the following license types:
- Named User—The default license type.
- Single Use—Available through license conversion when ArcGIS Pro is part of ArcGIS Desktop.
- Concurrent Use—Available through license conversion when ArcGIS Pro is part of ArcGIS Desktop.
Note:
It's possible to have a combination of different ArcGIS Pro license types.
Named User license
With the Named User license type, ArcGIS Pro core and extension licenses are assigned to members of an ArcGIS Online or ArcGIS Enterprise organization by the organization administrator. An ArcGIS Pro license is assigned automatically to members who have the GIS Professional user type. It can be assigned as an add-on license to members who have the Creator user type.
An organization member who has been assigned an ArcGIS Pro license uses their ArcGIS Online or ArcGIS Enterprise account credentials to sign in to ArcGIS Pro. The member can sign in to the application on any machine on which it is installed (up to three machines at the same time).
The application runs with the license level (Advanced, Standard, or Basic) specified by the organization administrator and with any extensions for which licenses have been assigned. The license type and level can be seen in the ArcGIS Pro Settings 
on the Licensing page.
Single Use license
A Single Use license authorizes one person to use ArcGIS Pro. That person can use the software on one computer at a time, while having it installed on a maximum of two computers.
If ArcGIS Pro has been purchased as part of the ArcGIS Desktop product suite, the license also authorizes the same person to use other ArcGIS Desktop applications—ArcMap, ArcCatalog, ArcGlobe, and ArcScene—in the same way.
A Single Use license can be transferred to a different computer deauthorizing the license on the currently authorized machine and repeating the authorization process on the new machine.
It is not necessary to sign in to use ArcGIS Pro with a Single Use license.
Concurrent Use license
A Concurrent Use license enables multiple users to share access to ArcGIS Desktop, optionally including ArcGIS Pro, from any computer on a network or a virtual machine. ArcGIS License Manager software, installed on a network computer, manages the distribution of a pool of shared licenses. The number of Concurrent Use licenses in the pool determines how many people can use the software at the same time. When a user starts ArcGIS Pro with a Concurrent Use license, the software sends a request to the license manager to determine if a license is available. The user can choose any available license level and extensions. At this point, the software is enabled and the number of available licenses decreases by one. When the user stops using the software, the license is returned to the pool.
A Concurrent Use license can also be borrowed from the license manager so that the software can be used for a specified time while a user is disconnected from the network. When a license is borrowed, the number of available licenses in the pool decreases by one. The user can return the license to the pool by reconnecting to the network. (The license will be returned automatically at the end of the specified borrowing time.)
It is not necessary to sign in to use ArcGIS Pro with a Concurrent Use license.