CPU vs Processor vs Core [closed]

In the book “Operating System Concepts”, CPU is defined as hardware that executes instructions and Processor is defined as physical chip and Core is defined as basic computational unit of CPU.

So, What is the difference between CPU and processor? Does core refer to an ALU? In what context can we use CPU and Processor? What does CPU refer to in multicore and multiprocessor systems? I am not able to visualize the differences.