Generally speaking, a gabbai (feminine: gabba’it) is appointed to serve to distribute honors for a service and to conduct (stage manage) some of the ritual.
Over time, similar jobs in various places and times have been done by a shamash or a sexton. Some places even have had “beadles,” but that leads to too much potential humor to mention it here.
Speaking of humor, a shamash can also mean an assistant to a rabbi (that’s me!), or the candle on a menorah that serves to light the others: in other words, a servant. Back to gabbai’im!
The word גַּבַּאי comes from the root gavah, to exact payment, and can also refer to the collector of synagogue dues or taxes. And through the ages there have been many kinds of gabbai’im, in charge of many things in society. But today we are talking about the gabbai’im at the services.
There is a floor gabbai who looks at the composition of the congregation and assigns any honors not previously assigned. For instance, s/he may see a person with a yahrzeit (annual commemoration of a loved one’s death) that day, or someone who has just returned from a journey, or a guest, and will offer an aliyah to that person. S/he may also, along with the ushers and greeters, make certain that the services are running smoothly overall and that the congregation is comfortable, with the proper books and information.
There are also two gabbai’im who tend the Torah service, assisting the ba’al keri’ah (in Yiddish the leyner, the person chanting), following along, calling up anyone who has an aliyah, making certain the scroll is rolled properly and taken care of, and assisting in the ritual in any way needed.
Maybe if we called them “beadles” more folks would learn and volunteer. Singing “We can work it out….” With a little help from my friends.