Up until fairly recently, microprocessors had only one central processing unit (core). The single CPU is produced on a sliver of silicon called a 'die' and this is packaged inside the integrated circuit.
For many years companies made faster and faster CPU cores as they competed to make the most powerful devices. But the faster they went, the hotter they got. Until they became so hot they no longer worked reliably - the silicon die itself was cooking.
The solution to improve performance without cooking the chip was to build more than one core within the integrated circuit and run those at a lower speed. It is then called a multi-core processor.
There are Duo-Core and Quad-core microprocessors available.
Of course you must have an operating system and software that can take advantage of each core, otherwise nothing is gained.