kiba 牙 (Fang)

In Japanese, kiba 牙 means "fang" or "tusk," and a fang is a long sharp tooth, typically the canine teeth. In real life, humans don't have fangs—since their canine teeth are relatively short—but various carnivorous animals do, including even domestic cats.

Amanojaku 天の邪鬼, example of cat with heterochromia, one blue eye one yellow eye, kin-me-gin-me 金目銀目.

Character: Amanojaku 天の邪鬼
Anime: Ghost Stories, Gakkou no Kaidan 学校の怪談 (Episode 1)

A cat with a gold eye and a blue eye, showing four fangs.

In manga and anime, some human and human-like characters do have fangs.

Meaning

The word kiba 牙 means long pointed teeth, and translates to English as either "fang" or "tusk." The difference between these two words in English is that a tusk grows out of an animal's mouth, while the fang does not.

tora no kiba
トラの牙
The fangs of a tiger.
Tiger fangs.
manmosu no kiba
マンモスの牙
The tusks of a mammoth.
Mammoth tusks.
kyuuketsuki no kiba
吸血鬼の牙
The fangs of a vampire.
Vampire fangs.
ooku no kiba
オークの牙
The tusks of an orc.
Orc tusks.

Since tusks are always out of the mouth, the following sentence only makes sense with fangs:

kiba wo muku
牙を剝く
To bare [one's] fangs.
- To expose one's fangs.
- With humans: to appear threatening, to show that you want to attack someone, typically not in the physical sense, but in the sense of being somebody's enemy.
- Similarly:
- shirome wo muku
  白目を剥く
  To bare [one's] sclera. (literally.)
  To open one's eyes wide. (in shock or anger.)

In anime, there are countless human characters that have fangs, however, most of them have just one single cute fang visible all the time, rather than two or four, which is actually a different sort of thing.

Sakura Hibiki 紗倉ひびき, example of anime fang, yaeba 八重歯.

Character: Sakura Hibiki 紗倉ひびき
Anime: Dumbbell Nan Kilo Moteru? ダンベル何キロ持てる？ (Episode 1)

This is NOT called kiba 牙 in Japanese, it's called yaeba 八重歯 instead.
See anime fang for details.

Examples

For reference, some anime characters with kiba 牙.

Manga: Killing Bites, キリングバイツ (Chapter 1, カーテンよりこっち側は見ない方がいい)

Context: Uzaki Hitomi 宇崎瞳 explains what is Killing Bites.
{kiba no surudoi} hou ga katsu
牙の鋭い方が勝つ
The side [whose] {fangs are sharp} wins.
The one with the sharpest fangs wins.
- no の - subject marker.
sore ga "Kiringu Baitsu" da
それが「牙闘」だ
That is "Killing Bites."
- In the manga, "killing bites," kiringu baitsu キリングバイツ, is spelled with the kanji for "fang," kiba 牙 and "to fight," tatakau 闘う, so literally "fang-fight." This is called gikun 義訓.