Lashes, also known as eyelashes, are the small wisps of hair that grow at the edges of the eyelids. They grow outwards in up to six layers on the edges of the upper and lower eyelids and serve three main functions: protecting the eye from debris, dust, and small particles; performing some of the same functions as whiskers do on a cat or a mouse in the sense that they are sensitive to being touched, thus providing a warning that an object (such as an insect) is near the eye (which then closes reflexively); and enhancing the appearance of the eye. The eyelid margin from which lashes grow is among the most sensitive parts of the human body, with many nerve endings enveloping the lashes, giving it sensitivity to light touch, enabling it to trigger the blink reflex when touched. The number of individual lashes on the upper eyelid is typically 90 to 160, and on the lower eyelid 75 to 80. Lashes cannot be increased after birth because all follicles develop during embryogenesis.

It is important to note that "lash" can also refer to a sharp cutting blow from a whip or other flexible object, the flexible end or ends of a whip, or a cutting or hurtful blow to the feelings, as one caused by criticism.

Eyelash extensions are also a popular cosmetic procedure where semi-permanent fibers are attached to natural eyelashes to make the lash fringe look longer and fuller.