Actually I thought it was et alia, not et alii.
However, I'd just guessed that's what it is, while you probably actually learned it.
Its just as correct - its a matter of gender.
alii - male..
aliae - female..
alia gender neutral. Though I find I'm debating myself on what the DUmmy would prefer - Alii - would be a direct hit at men, which DUmmies would like, yet alia has no gender reference, which they also approve of. Somewhat torn on this..