From the Latin nomen, name. Nominalism is a doctrine that is dealing with the status of universals. For the nominalist, individuals are only real, and the universals are simply names or sounds of the voice.
The universals are predicative terms for an unlimited number of objects. One can apply the same term to different things, such as a human being to Plato, Aristotle, and in fact everyone else.
The ontological status of beings such as Plato and Aristotle is considered unproblematic, they are individuals and as such, they are real or actual. (The ontological status of beings or signifiers, that is, anything that can be signified or identified, refers to their position in reality.)
But what about the ontological status of universals? What position do they have? According to nominalism, universal terms are pure vocal sounds or sentences, the only basis they have is how they are pronounced. In contrast, realists maintain that at least some universals have their foundations in reality.
When someone says of Plato or Aristotle that they are human beings, he claims this not simply on the basis of a linguistic convention, but on the basis of some objective features shared by different individuals.
In the writings of Charles S. Peirce, nominalism has many meanings, including the doctrine that existence or actuality is the only state of being. He rejects this and many other statements of nominalism.