One 64-bit usearch license terms allows you to run one usearch "process".
A "process" is a technical term used in Linux and other operating systems. Informally, it is a running copy of a binary program. The top and ps ("process status") commands in Linux and OSX show one line for each process.
Multi-threading is supported within a process. In other words, a single process can run multiple threads (if supported by the command).
A 64-bit license allows you to run one process. If top or ps shows usearch N times, then you are running N usearch processes and you need N licenses. It doesn't matter if these processes are all running on one computer or on different computers, the same principle applies.
It is OK for people in a group to share the license if they make sure that only one process is running at any given time.
It is not OK for one person to start many processes, e.g. on a compute cluster, unless they have multiple licenses.