Kraeusen is the name for the darker, spotted, almost rocky head of foam that forms on the surface of the wort during the fermentation period. It often forms a ring on the fermentation vessel even after the beer has completed fermentation.
The term alcohol when applied to beer is really just a synonym for either ethyl alcohol or ethanol. Most craft beer styles range between 3.2% to 10% alcohol by volume (ABV), although some are even lower or higher than that.
Bottle conditioning is the process through which beer is naturally carbonated in the bottle as a result of fermentation. Usually this is accomplished by adding a priming sugar during the bottling process.
A naturally occurring soft resins in hops. Alpha Acids are converted during wort boiling to iso-alpha acids, which adds bitterness to beer. Over time alpha acids will age out (through oxidation) and bitterness will lessen.