It used to be that use of the male gender would encompass both feminine and neuter genders. That is no longer acceptable practice and it has triggered some interesting quirks. Consider the sentence: if you see someone without a mask, call him or her out. This is correct language but a mouthful. What has crept into informal acceptance is the use of the gender-neutral “they, them, etc.” with the singular noun: if you see someone without a mask, call them out. For the classical stickler it would be better to re-write the sentence: call out anyone you see without a mask. But God forbid we let “your” become acceptable spelling for “you’re”.
Singular they is the use in English of the pronoun they or its inflected or derivative forms, them, their, theirs, and themselves, as an epicene singular pronoun. It typically occurs with an unspecified antecedent, as in sentences such as: “Somebody left their umbrella in the office.” Wikipedia
