What's the meaning of "tab" in the following sentence? And they provide an environmentally friendly way to keep tabs on any group of residents who might be indulging in one too many.Context: 20141223-Dumpster Diving Provides Drinking Data Trash cannot talk, obviously. But your recycling can still say a lot about you. For example, the bottles you put in the blue bin can reveal how much alcohol you drink. Or so say scientists from the Ohio State University. They set up a recycling program as a way to track alcohol consumption at a senior center in San Diego. They pore over their data in the journal Alcoholism: Clinical and Experimental Research. Managers at this particular housing complex had been concerned about alcohol abuse among their older residents. Binge drinking can be as bad for these seniors as it is for those in college. So researchers placed recycling bins on five floors at the center and checked them twice a week for more than a year. They counted all the beer, wine and liquor bottles and calculated how much hooch the folks at the home were putting away. The boozing peaked around holiday time and in the days after the residents received their social security checks. The results could allow social workers to target their prevention programs to times when their residents are most likely to tipple. And they provide an environmentally friendly way to keep tabs on any group of residents who might be indulging in one too many.