A flashlight is a light that's small enough to hold in your hand and carry around. When you're camping, it's useful to bring a flashlight so you can find your sleeping bag in the dark tent.
Most flashlights are powered with batteries, although some of them can be charged in the sun and use the stored solar energy for power. All flashlights are portable, basically small lamps that fit easily in your hand, your pocket, or your backpack. In Britain, a flashlight is often called a torch. The earliest versions of flashlights were invented around 1899.