Ok this is confusing, in the old days a PAR30 meant and halogen light that was 30 1/8″ of an inch (that is 30 * 0.125″ = 3.75″ wide). And they use the medium sized socket called the E26 base you see in a regular light bulb (technically that is called an A shape with E26 base). PAR meant Parabolic Aluminum Reflector and you could get it in narrow (5-10 degrees all the way to wide beam (33-45 degrees) and then ultra-wide (45 degree). It can be used outdoor.
The BR30 is an incandescent light and BR means bulged reflector come in just 45 degree beam. There is also an R30 which is narrower. It is only indoor.
The also come in colors from soft white (aka 2700K) to cool white (4400K) to daylight (5000K+) with the traditional light bulb with that nice orange glow at soft white.
But what about an LED, which is what everyone should get? Well they come in PAR30 and BR30? The big difference now is that LED PAR30 can be as high as 70,000 hours while the LED BR30 are 25,000 hours, so it makes sense to get the LED PAR30.
So for instance the TCL BR30 Dimmable is rated at 25K hours for $3.33 per bulb on Amazon. But, the most of the PAR30 LEDs are basically the same at 30K hours but they do work outdoor, so the main difference is that they are outdoor and you can tune the beam width.
Finally they do need LED compatible dimmers fyi.