Question about L3 cache on a intel processor?

i was checking out some information on wikipedia this morning, realized that Intel i3 is a dual core processor, however that was not my goal for posting a question here, my question is while am looking through the article, i saw something name "L3 Cache 4mb". so what exactly it is ? what does it do?

Thank you very much:)

P.S i searched in yahoo answer realized that L3 does not use for processor, then why is that they have "L3 Cache" on wikipedia?