"Bunny Ears," usamimi うさみみ

In Japanese, usamimi うさみみ means "bunny ears" or "rabbit ears." It's a portmanteau combining the words usagi 兎, "bunny," "rabbit," and mimi 耳, "ears." In other words: it's an abbreviation of usagi-mimi 兎耳.

Like "cat ears," nekomimi 猫耳, usamimi is a specific type of kemomimi ケモミミ, and normally refers to headbands featuring bunny ears, or characters featuring bunny ears, rather than the actual ears of a bunny.

Nakano Azusa 中野梓, example of bunny ears, usamimi うさみみ.

Character: Nakano Azusa 中野梓
Anime: K-On!, Keion! けいおん！ (Episode 9)

Examples

For reference, some examples of characters wearing usamimi.

Shirogane Miyuki 白銀御行, Fujiwara Chika 藤原千花, Shinomiya Kaguya四宮かぐや, example of "bunny ears," usamimi うさみみ.

Left: Shirogane Miyuki 白銀御行
Middle: Fujiwara Chika 藤原千花
Right: Shinomiya Kaguya 四宮かぐや
Anime: Kaguya-sama wa Kokurasetai? ~Tensai-Tachi no Ren'ai Zunousen~ かぐや様は告らせたい？～天才たちの恋愛頭脳戦～ (Season 2) (Episode 3)

Natsume Zange 夏目残夏, example of kitsune-me キツネ目, usamimi うさみみ.

Character: Natsume Zange 夏目残夏
Anime: Inu x Boku SS, 妖狐×僕ＳＳ (Episode 6)

Plus Suit

Often, usamimi is worn together with a corset, pantyhose, tail, and detachable collar and cuffs. This is called a bunny suit.

See Bunny Girl for details.

Kamiigusa Arisu 上井草有栖, Asagaya Minoa 阿佐ヶ谷未乃愛, example of "bunny girl," banii gaaru バニーガール.

Left: Kamiigusa Arisu 上井草有栖
Right: Asagaya Minoa 阿佐ヶ谷未乃愛
Anime: Animegataris, アニメガタリズ (Episode 2, Stitch)

Natural

An example of natural bunny ears:

Kuro-Usagi 黒ウサギ, Kasukabe You 春日部耀, example of "bunny ears," usamimi うさみみ.

Left: "Black Rabbit," Kuro-Usagi 黒ウサギ
Right: Kasukabe You 春日部耀
Anime: Mondaiji-tachi ga Isekai kara Kuru Sou Desu yo? 問題児たちが異世界から来るそうですよ？ (Episode 1)