Standard Rate of Measurement (SRM) is a method to measure a beer’s color. The scale for the lightest beer generally starts at 2 and goes up to the darkest stouts at 40+. SRM is actually a measure for the amount of light that gets absorbed by beer.
Gravity is typically referring to the specific gravity (SG) of the beer. SG is the measurement of how dense a liquid is compared to water and how much sugar is in solution of the wort. Using specific gravity is a means for many brewers to determine alcohol content. This is done by using the difference of the beers original gravity (before fermentation) and final gravity (post-fermentation). The difference is the sugars consumed by the yeast that has been converted to alcohol on carbon dioxide.
International Bittering Unit (IBU) is a standardized method to calculate the bitterness of a beer based on the battering values of hops. This scale ranges from 0-100+, although in most cases beer cannot physically exceed 100. Light Lagers can range from approximately 5-12 IBUs, while Double IPA’s can push the limits of 100 IBUs.
Alcohol by Volume (ABV) is expressed as a percentage of alcohol based on the ration of a column of alcohol per volume of beer. This is commonly the preferred method of expressing alcohol content, the other being alcohol by weight (ABW).
Flocculation is the tendency of yeast cells to aggregate together, forming a multicellular mass and sedimenting rapidly from the suspended medium or rising to the surface. Yeast flocculation is a complex phenomenon occurring in brewer's yeast under various conditions near the end of the fermentation process.
Attenuation refers to the conversion of sugars into alcohol and carbon dioxide by the fermentation process; the greater the attenuation, the more sugar has been converted into alcohol. A more attenuated beer is drier and more alcoholic than a less attenuated beer made from the same wort.