A circle is 360 degrees, so 90 degrees would be 1/4 of a circle. Place your thumb and forefinger so it looks like an L. That angle is 90 degrees. Imagine the flashlight at the joint between your thumb and forefinger. The beam pattern is that L shape. The closer you bring your thumb and forefinger together, the narrower the beam, 80-70-60-50-45, etc.
80 degrees would be a tiny bit narrower than 90 degrees, and that's the area you would see, from left to right, as you point the flashlight straight ahead. A light with 120 degree coverage would be wider from left to right (and up and down typically), while a light with a 45 degree beam spread would show less area, smaller circle.
With most flashlights, that bright central area is called the spot, and a 10 degree hot spot is fairly narrow, while a 20 degree hot spot would be a bigger circle. That hotspot is surrounded by another, usually less bright circle of light. You will see that referred to with several different terms. I call it the "fill" or "spill".
So, a 10 degree hot spot, with a 80 degree spill, is a pretty typical beam pattern. A 40 degree hot spot, with a 120 degree spill would mean you'd see a fairly broad, bright central area, and a fairly broad, wide spill around that.
However, it's also important to understand the ratio of light between the hotspot and the spill. Some beams will have a bright hot spot, and a very dim spill, while others will have a softer, broader hotspot, and an only slightly dimmer spill.
The narrow area directly surrounding the hotspot is called the corona, and that is the transition area between the hotspot and the spill. On some lights that is a very sharp transition, while on other lights it tapers gradually from the hotspot into the spill.
The beam pattern, either wide or narrow can have a great effect on the perceived brightness of a light. Say you have two lights, and they both put out exactly the same amount of light, but one has a wide 120 degree beam, while the other one has a narrow 45 degree beam. The light with the wide 120 degree beam is taking the same number of photons exiting the light and spreading them out over a greater area, so it will often seem less "bright", while the other light with the 45 degree beam is taking those same photons and concentrating them into a much smaller area, so it will appear "brighter". This is the difference between "LUX" and "LUMENS".
Anyway, that's probably more than you wanted to know, but it's all very important in helping you pick the right light for your particular purpose, so keep reading and asking questions........ and by the way, welcome to the forum
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Oh, here is a video that talks a bit about beam patterns:
http://www.youtube.com/watch?v=f4L1uIcbalQ#t=43
Have fun!