noun
almond-shaped eyes; slit eyes
Describes eyes that are horizontally long and narrow, with the outer corners slanting upward; often considered an attractive feature in Japanese aesthetics.
彼女は切れ長の目がとても魅力的だ。
Her almond-shaped eyes are very attractive.
切れ長の目は、涼しげな印象を与える。
Almond-shaped eyes give a cool, refined impression.
一重 means single-lidded eyes, which can sometimes appear narrow, but 切れ長の目 specifically refers to the elongated, upward-slanting shape regardless of eyelid type.
Compound of 切れ長 (long and narrow, literally 'cut long') + の (possessive particle) + 目 (eye). The exact historical derivation is uncertain, but the phrase is conventionally used to describe a specific eye shape.