A processor, or CPU, is the brain of a computer, responsible for executing instructions and performing calculations. Key features include the number of cores, which allows for multitasking by running multiple processes simultaneously, and clock speed, measured in gigahertz (GHz), which indicates how fast the processor can execute instructions. Another important feature is cache memory, which stores frequently accessed data for quick retrieval, improving overall performance. Additionally, modern processors often support technologies like hyper-threading, enabling each core to handle two threads at once, further enhancing efficiency and speed in processing tasks.