Although our lookups are often driven by events in the news,
the dictionary is also a primary resource for information
about language itself, and the shifting use of they has
been the subject of increasing study and commentary in recent
years. Lookups for they increased by 313% in 2019 over the
English famously lacks a gender-neutral singular pronoun to
correspond neatly with singular pronouns like everyone or
someone, and as a consequence they has been used for this
purpose for over 600 years.
More recently, though, they has also been used to refer to one
person whose gender identity is nonbinary, a sense that is
increasingly common in published, edited text, as well as social
media and in daily personal interactions between English speakers.
There’s no doubt that its use is established in the English
language, which is why it was added to the Merriam-Webster.com
dictionary this past September.