A device placed in or over the mouth to prevent speech or noise. Often used in BDSM contexts, hence the vulgar label. Compare 猿轡 (さるぐつわ), a similar gag.
See also: 猿轡
She was gagged and couldn't make a sound.
Mixed kana-kanji spelling; may be easier for learners.
Compound of 口 (くち, 'mouth') and 枷 (かせ, 'shackles, fetters'). The kanji 枷 is not commonly used in modern Japanese outside of this word and a few others.