What do you think what is cache memory?
Our electronic definitions web site has answer for that as well:
is an extremely fast part of main store.
Another definition of cache memory:
Temporary memory set aside to store the information that is accessed most frequently. The Pentium processor has 8Kb of inbuilt cache. This can be further speeded up by a secondary cache typically 256Kb. Part of your DRAM is often used to cache your hard disk.