The tag alias #46990 heterochromia_iridum -> heterochromia has been approved.

Reason: same thing

Could possibly also be reversed, but heterochromia has been in use for a much much longer time.

EDIT: The tag alias heterochromia_iridum -> heterochromia (forum #294961) has been approved by @Millcore.

The wiki entries say different things:
heterochromia_iridum - "two colors in one Iris"
heterochromia - "includes characters with separate colored eyes"

The former wouldn't include posts like this:
post #496734 post #32779

But would include posts like this:
post #2223809 post #2333155

Granted, scientifically speaking they're the same thing, but maybe it would be worth it to distinguish multiple colors in one eye vs each eye being its own color. But it seems there's a bunch of mistagging of heterochromia_iridum on characters who have single-colored irises (just with each iris being a different color), so maybe it's not worth trying to distinguish them.

Interesting, I should've read the wiki, but since these are both scientific terms meaning the same thing I still think they should be aliased. There's a two_tone_eyes tag that those examples would probably fit better under.

These should be aliased. They're the same thing, just a shortened name. I would've said to make sectoral or partial heterochromia a tag for those with multiple colors in the same eye, but as faucet pointed out, two_tone_eyes and multicolored_eyes exist (and for that matter, central_heterochromia is already aliased to multicolored).

The tag alias heterochromia_iridum -> heterochromia (forum #294961) has been approved by @Millcore.