LED MR16 spotlights offer a low voltage alternative to the standard GU10 spotlights. They are most commonly used in integrated fixtures and fittings, particularly in kitchens, where they're often installed in cooker hoods and under cabinets, and are sometimes called GU5.3 spotlights, which refers to their particular fitting.
As they are low voltage bulbs, they are not compatible with standard mains voltage fittings, and while the bulb itself looks very similar to a GU10 bulb, MR16s can be distinguished by their fitments, which look like two small spikes protruding from the base of the bulb.
As they are often used in integrated lights, you may need to disassemble the fitting to access the bulb itself. MR16s are easy to install, though, as they simply slot into the fitting once you have access. If you're not sure about accessing integrated lights, we would advise you to consult a qualified electrician.