I guess you mean what are those things in general?
Clock speed: How many times per second can the processor's parts (arithmetic & logic units ...) operate on sets of numbers. Each clock cycle, all the pipeline stages that have something to operate on do so. The job of good processor manufacturers and compilers is to make sure as many stages as possible are filled each cycle such as to minimize the number of cycles until a certain amount of work is done.
Front-Side Bus (FSB): The speed at which information can be relayed between the main memory (RAM) and the processor (CPU).
Frequency is the clock speed.
Core in these forums is usually referring to the design of the processor. A 2.4GHz Conroe (Intel Core2) is much better than a 2.4GHz Northwood (Intel P4) due to the different design of the processor - components are organized differently, there are different amounts of each type of unit, the pipeline stages are different...
Jo