... it does have a place amongst the terms and slang used by
photographers (nifty-fifty is another example, if you're versed in
photography you know what it means, but everyone else gives you a
Maximum aperture - most 'nifty fifties' have a maximum aperture of around f/1.8. In comparison to most cheap consumer zoom lenses, that's about three stops wider/faster than a typical 18-55mm f/3.5-5.6 when set at 50mm.
Mature optical design - The 'nifty fifty' is not new. It's been around for a long time. The design of 50mm lenses for cameras with diagonals of around 44mm (please see note ²) is quite mature.
Relatively compact design - They're small and lightweight compared to many other lenses. The Canon EF 50mm f/1.8 STM (Canon's current nifty fifty) is 5.6 ounces and about two inches long. The Canon EF 50mm f/1.2 L is 19.2 ounces and almost three inches long.
Value - For the price it is hard to beat the optical quality provided by most 'nifty fifties'. In terms of image quality "bang for the buck" most 'nifty fifty' lenses from the various manufacturer are some of the best values around. But they are far from some of the best prime lenses around. Perhaps one reason so many photographers claim the 'nifty fifty' lenses are super sharp is because they're the only prime lenses they've ever used and they are usually better optically than their consumer grade zoom lenses set at 50mm.
¹ A prime lens is a lens with only one focal length. No zoom. ² 35mm film has a width of 36mm and a height of 24mm for a diagonal of between 43mm and 44mm. ³ The distance from the image plane to the lens mounting flange. Sometimes called the flange focal distance.
They are typically (but not always) small lenses. Compact, easy to carry.
They are typically a good focal length either on full frame or crop frame cameras. On crop frame they make good head-and-shoulders or head portrait lenses. On full frame the field of view is wider, and but still offers good portrait lens angles, or street photography angles.
They are wide aperture lenses, making them useful for low light or shallow depth of field photography - the later being again useful for portraits.
Many systems have relatively cheap entry level f/1.8 50mm lenses, making them a popular entry into wide aperture photography.
The small size means they're easy to carry around with another lens, making them really handy to keep around for photo opportunities that pop up. Personally I'd be loath to travel without one if at all possible, particularly to a social event.
Nifty-fifties exist for most DSLR and MILC platforms. On the 4/3 and micro 4/3 systems they would be slightly longer for field of view, but still offer a lot of possible options, but fewer social shooting opportunities.
It is ( a typically low priced) 50mm prime lens sold in a prosumer camera kit. The choice of 50mm is because this is considered the "normal" focal length lens for a 35mm camera. This was often the focal length lens used in portraiture photography when using a 35mm film camera.