Sea shanties (singular "shanty", also spelled "chantey"; derived from the French word "chanter", 'to sing') were shipboard working songs. Shanties flourished from at least the 15th century through the days of steam ships in the first half of the 20th century. Most surviving shanties date from the 19th and, less commonly, 18th centuries.
In the days when human muscles were the only power source available aboard ship, sea shanties served a practical purpose: the rhythm of the song served to synchronize the movements of the sailors as they toiled at repetitive tasks. They also served a social purpose: singing, and listening to song, is pleasant; it alleviates boredom, and lightens the burden of hard work, of which there was no shortage on long voyages.
Most shanties are "call and response" songs, with one voice (the shantyman) singing the line and the chorus of sailors bellowing the response (compare military cadence calls). For example, the shanty "Boney":
Shantyman: Boney was a warrior,
All: Way, hey, ya!
Shantyman: A warrior and a terrier,
All: Jean-François!
The "pulls" would be on the last syllable of the response in each line.