(countable) An appearance of light, especially one which is indistinct or small, or short-lived.

(countable, figurative) A noun "gleam" represents an indistinct sign, a bright but short-lived appearance, or a look of joy or liveliness on one's face.

(transitive) Chiefly in conjunction with an adverb: to cause (light) to shine.

(intransitive) Shine or glisten in an indistinct or intermittent manner, and can also be used figuratively to describe something that is strongly but briefly apparent.