As an expert in the English language, I can confirm that the word "their" is a plural pronoun, typically used to refer to something that belongs to or is associated with more than one person or thing. However, in modern usage, "their" can also be used as a singular pronoun, especially when the gender of the person is unknown or when the person prefers a gender-neutral pronoun.

Here's the answer with the key term in red:

Their can be used as a singular pronoun, especially in contexts where gender neutrality is preferred or when the gender of the individual is not specified.

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Because he is no longer accepted as a generic pronoun referring to a person of either sex, it has become common in speech and in informal writing to substitute the third-person plural pronouns they, them, their, and themselves, and the nonstandard singular themself.read more >>