(see also: The Voices)
The "Hivemind", also known as "the mob", is slang used by the Twitch Plays Pokemon community referring to players in the stream. The name comes the concept of Collective Consciousness or Swarm Intelligence which is explained as a set of beliefs or ideas that create a unified force within a given society (In this example, TPP). More simply, it refers to the behaviour of each individual involved in the stream and how the majority of players are all attempting to reach the same goals, and so collectively pool their efforts into achieving something.
The use of the word Hivemind is not limited to just TPP and it has been frequently used to describe other large societies on the internet. The reason it works so well as a descriptor for TPP is that the input list somewhat resembles that of a swarm, which could be easily associated with common insects that are known to operate in colonies or hives such as bees or ants. The visual identifier and the behavioural identifier both give presence to the concept of a collective consciousness within the stream, or a hivemind.