Nominalization is a process whereby a word that belongs to another part of speech comes to be used as a noun. For example, an adjective can act as a noun referring to people who have the characteristics denoted by the adjective. For example,
This legislation will have the most impact on the poor.
The race is not to the swift, nor the battle to the strong.
The Socialist International is a worldwide association of political parties.
In the above examples, poor, swift and strong refer to people with those qualities. International refers to the organization of worldwide socialist parties