The Central Processing Unit, or CPU, and often called the “brain” of a computer, is the most important part of a system. CPU speed is measured in hertz (Hz), or cycles per second. Current processor speed is measured in GHz, or billions of cycles per second.
Modern systems can have more than one CPU, and each CPU in turn can have more than one CPU core (which, in turn, might be split up into virtual cores).
For a typical SQL Server workload, single-core speed matters. It is better to have fewer cores with higher clock speeds than more cores with lower speeds, especially for non-Enterprise editions.