These indoor flood and spot lights have been the mainstay of household lighting for recessed and track lighting all over the world. While they are incandescent reflector bulbs, they are also halogen; as a result they are slightly more expensive to buy, but they are less expensive to run over their lifetime. Originally the R style bulb was the only style, but government regulations on energy efficiency elevated the BR light bulbs into prominence.
The real difference between the two types is the bulging portion on the BR bulb where the neck meets the wider reflector shape. The bulbs are truly interchangeable in every way, so if you have an R bulb you are trying to replace, and you see a BR light bulb in a similar wattage and size, you may choose to use that as well. Make sure to consider the distance across your bulb and the overall length to ensure it will fit into your fixture.
While some new construction is converting directed lighting to more energy efficient CFL floods, the R and BR light bulbs can be found in millions of rooms all across America, from small one bedroom apartments all the way up to the larger and more luxurious homes and condos.