"The magic number 7, plus or minus 2" is a popular phrase from a George Miller research paper referring to how many pieces of information people can process (from 5 to 9). it's also a myth as the research paper was actually a talk Miller gave.
Further research done by Alan Baddeley and Nelson Cowan shows that the magical number is actually 3 or 4 so long as there aren't any distractions.
Slide 2
Using "Chunks" to Expand Your Memory
"chunking" information together into groups is a strategy used to help remember more.
For example: phone numbers!
704-333-2443
instead of having to remember 10 separate numbers; you have 3 "chunks" with 4 or less in each one therefore it is easier to remember.
Research shows that 4 item rule applies to long-term memory too. George Mandler showed people could memorize information in chunks and remember it if there were one to three items in each one as the number of items increased, the ability to remember decreased.
2 Japanese researchers showed that the rule can even apply to chimps!