OK..............a very crude and simple explanation.............(If you need more detail, please follow up)

Cache is a memory store where data or instructions that are most likely to be used next are stored...........this makes them happen faster, and improves the performance of the machine ( in theory )

If you have "on chip" cache , this is good, "on core is better"................it happens faster............the smaller the value, the closer to the core it is.

I have an old machine with this fine, erect 256Kb cache memory card.............it runs like a rocket compared to its like devices............It is a PI/133 and will run within 12% of a PII/266.............but I have "developed" it for sentimental reasons..................

Basically, a "cache" is a "store" (of data) that can be readily accessed.

Cheers