E is non Japan NTSC code, P is PAL which is used by (almost) all of the rest of the world.
(taken from wiibrew)
A All regions. System channels like the Mii channel use it.
D German-speaking regions. Only if separate versions exist, e.g. Zelda: A Link to the Past
E USA and other NTSC regions except Japan
F French-speaking regions. Only if separate versions exist, e.g. Zelda: A Link to the Past.
I Italian-speaking regions. Only if separate versions exist, e.g. Pokemon Snap. Unofficially used by The Homebrew Channel 1.0.5 and newer.
J Japan
K Korea. Unofficially used by DVDX 2.0.
L Japanese Import to Europe, Australia and other PAL regions
M American Import to Europe, Australia and other PAL regions
N Japanese Import to USA and other NTSC regions
P Europe, Australia and other PAL regions
Q Korea with Japanese language.
S Spanish-speaking regions. Only if separate versions exist, e.g. Pokemon Snap
T Korea with English language.
X Not a real region code. Used by DVDX 1.0 and The Homebrew Channel versions 1.0.4 and earlier.
But for the most part only A E J P and K are used.