A flashlight (sometimes called a light) was a portable hand-held light source that can illuminate darkened areas.
In the year 2152 Alana Hart was inspecting the starboard launch tube with a flashlight. (ENT novel: What Price Honor?) Later in that same year, Hoshi Sato used a flashlight while crawling through the air vents on the Enterprise (NX-01). (ENT novel: Shockwave)