Hey Elroy,
Bloom is the "light bloom" feature in the FSX settings. It makes light, well, bloom and could make it a little more realistic. However, it will kill your frames
Absolutely, the bloom is that particular graphical effect that makes everything that shine much more beautifull. That includes the sun, the runway lights, the aircraft lights, and the sun reflections on planes and water. The effect is really looking nice, but unfortunately it has a big performance hit in DX9 mode. In DX10 mode the performance hit is reduced.
There is also an alternative bloom effect, which works like an external module. This one works with FSX (both with FSX and FS9 planes) and also FS9, and even some other games as well. It brings bloom as well as some kind of HDR effect (like in Test Drive Unlimited for example). See my signature for more details.