Technically, MSG is supposed to be the "extra" taste area they didn't know about/ teach in school. So although it seems salty, it's actually the savory flavor. MSG is found in just about every single food you eat that has that "savory" flavor.

The "Extra" taste is called Umami: http://en.wikipedia.org/wiki/Umami

Also -- despite what you may have learned in school -- the taste buds aren't mapped to areas: http://en.wikipedia.org/wiki/List_of_common_misconceptions (Search for Taste for links to the relevant sources)

To clarify, since your parent didn't actually misspeak-- There are actually only five main tastes your taste buds can detect. They just aren't organized by location.

To the best of my knowledge, MSG isn't actually found in most sources of umami, but it's an excellent source of that flavour.

Well-known umami-tasting foods include red meat, cheese and other fermented products, and tomatoes. None of these contain MSG directly (tomatoes get their umami from glutamic acid, according to umamiinfo.com). However, MSG can be used to add more umami flavour, which acts as a flavour enhancer.

MSG basically IS glutamic acid, with Na+ ions.

"MSG is the sodium salt of glutamic acid" http://en.wikipedia.org/wiki/Monosodium_glutamate

Good point, and why it's an indispensable seasoning.