Some processors have a dual core, single chip that appears to be two CPUs within the Oracle kernel (the Oracle kernel determines the number of CPUs on a system during start-up). This is the case with Intel Hyper-threading, where the number of physical CPUs doubles when running on Linux or Windows with a hyper-threading setting of OS or BIOS.
Oracle will charge a CPU license fee for the extra cores in multiple core CPUs. Therefore, you will need to license for each CPU core in multiple core CPUs, meaning that a hyper-threading CPU is considered a single CPU for licensing, but a dual core CPU is considered 2 CPUs for licensing.
However, when Oracle audits/asks the OS how many CPUs are in the system, the OS just reports the total number of logical CPUs. In the case of Intel Hyper-threading, if the one core looks like two processors, then it is counted as two; therefore, two separate licenses are needed.