A Brit’s-eye view …!
A typical torch was/is a bundle of burning oil- or wax-soaked rags tied to a pole (enabling it to be portable) and set alight to be used for constant (if a bit smelly and smokey!) illumination. The modern portable equivalent, using batteries and an incandescent bulb, is therefore aptly described as a ‘torch’.
However, the battery-powered version also affords switching on and off the illumination in rapid succession – useful for signalling in Morse Code, say. So its description as ‘flashlight’ is equally as valid, irrespective of the duration of a ‘flash’.
The advent of LED versions with tiny round batteries, of course, means that they don’t even have to be torch-shaped any more, though the other properties remain!
‘Taschenlampe’? I really like that word – it sounds to English ears as though it defines a lantern powered by sneezing!