Provide the definition of a pronoun.
A word that can function by itself as a noun phrase and that refers either to the participants in the discourse (e.g., I, you) or to someone or something mentioned elsewhere in the discourse (e.g., she, it, this).
Complete the following task based on the instruction and optional input provided.### Instruction:
Provide the definition of a pronoun.

### Output:
A word that can function by itself as a noun phrase and that refers either to the participants in the discourse (e.g., I, you) or to someone or something mentioned elsewhere in the discourse (e.g., she, it, this).