A groundling was a person that frequented the Globe Theatre

Globe Theatre

The Globe Theatre was a theatre in London associated with William Shakespeare. It was built in 1599 by Shakespeare's playing company, the Lord Chamberlain's Men, and was destroyed by fire on 29 June 1613...

 in the early 17th century who was too poor to pay to be able to sit on one of the three levels of the theatre. By paying one penny, they could stand in "the Pit", also called "the Yard", just below the stage to watch the play. Standing in the pit was uncomfortable, and people were usually packed in tightly. The groundlings were commoners who were also referred to as stinkards or penny-stinkers They were known to misbehave and even throw food such as fruit and nuts at characters they did not like. They would watch the plays from the cramped pits with sometimes over 500 people standing there.

There might also be "cut-purses" in the crowd, who would cut the piece of string that attached a purse to a woman's clothes and snatch the purse without the women being aware of the theft.
The gentry would pay to sit in the galleries often using cushions for comfort. Rich nobles could watch the play from a chair set on the side of the Globe stage itself. Theatre performances were held in the afternoon because there was limited artificial lighting. Men and women attended plays, but prosperous women would often wear a mask to disguise their identity. The plays were extremely popular and attracted vast audiences to the Globe - the audience capacity was over 1500 people and this amount increased to 3000 when people mingling outside the grounds. In 1599, Thomas Platter

Thomas Platter

Thomas Platter was a Swiss humanist scholar and writer.His sons Felix Platter and Thomas Platter the Younger both studied medicine, a thwarted ambition of Platter's own early life...

noted the cost of admission in his diary:

There are separate galleries and there one stands more comfortably and moreover can sit, but one pays more for it. Thus anyone who remains on the level standing pays only one English penny: but if he wants to sit, he is let in at a farther door, and there he gives another penny. If he desires to sit on a cushion in the most comfortable place of all, where he not only sees everything well, but can also be seen then he gives yet another English penny at another door. And in the pauses of the comedy food and drink are carried round amongst the people and one can thus refresh himself at his own cost