The term "lobbying" means for a group of people with a certain cause in common to rally together in order to bring attention to that cause. They are often lobbying before congress or some entity who can do something about their cause such as make abortions legal or illegal. They are ultimately seeking to influence people, politicians or public officials to see their side on a particular issue at hand.
The group may protest, carrying signs for their cause and chanting slogans. Or, they may just assemble and draw attention from the media as well as potlitical attention. They feel very strongly about what they believe in so they are not afraid to spend countless hours and even money rallying and organizing. Causes can vary but the main thing is that they draw attention to the cause from the powers that be who can make a difference if persuaded.