"Their" is a possessive determiner in the English language. It signifies that something belongs to or is associated with a group of people, animals, or things. For instance, in the sentence "He gave them their coats," "their" indicates that the coats belong to the group referred to as "them."
In addition to indicating possession, "their" can also be used to refer to a single person when the gender is unknown or to avoid specifying gender. An example of this usage is "One of the students has left their book behind," where "their" is used instead of "his" or "her" to maintain neutrality.
"Their" is a key element in inclusive language, allowing for a more gender-neutral approach in writing and speech. This usage has become increasingly common and is widely accepted in modern English.
For more detailed information and examples, you can refer to reputable dictionaries like the Cambridge Dictionary, Collins English Dictionary, and Merriam-Webster.