Explanation: Threads

This is the number of logical CPUs in the system, which is equal to [Num physical packages] x [Num cores per physical package] x [Num logical threads per core]. The latter is more than one, when the CPU has Hyper-threading.

E.g., a triple-core, non-HT processor as the Phenom X3 has 3 threads. A quad-core HT processor as the Core i7 has 8 threads. If you get four quad-core Xeon processors in a single PC, you will get 16 threads.