Parshmen
The parshmen are a docile, enslaved people found throughout Roshar in Brandon Sanderson's The Stormlight Archive. Long treated as little more than beasts of burden, they are in truth a dormant form of the singers, the native sapient people of Roshar, severed from their natural rhythms and forms.
Nature
Parshmen have marbled red-and-black or red-and-white skin and were, for most of recorded history, regarded as mute, passive, and incapable of independent thought. They performed menial labor across Vorin society and elsewhere, owned and directed by humans. Their apparent docility led most Rosharans to assume they were simply a kind of useful animal.
The truth of the singers
In reality, the parshmen are singers, the same people known on the Shattered Plains as the listeners or Parshendi, locked into a powerless "slave form" or dullform and cut off from the spren-bonds that grant the singers their other forms and their connection to the rhythms. This severed state was a consequence of ancient events tied to humanity's wars against the singers and the influence of Odium.
Awakening
With the coming of the Everstorm, a storm called into being by Odium's power, the parshmen across Roshar are awakened. Touched by the new storm, they regain forms, intelligence, and the rhythms of their people, transforming overnight from a docile slave caste into an aware and often vengeful population. This awakening upends Rosharan society and becomes a central element of the war against Odium.