From the National AAUW website:

Gender fluidity. Gender exists on a spectrum, with each of us lying somewhere along that continuum. Our gender expression can be seen in how we look, how we dress and how we describe ourselves — right down to pronoun usage. The traditional use of he/him, she/her reflects a binary notion of gender. This excludes people who don’t identify in either of these two ways. Some people use they/them pronouns or other gender neutral options such as zie/zir. It is best to always ask new people you meet what their pronouns are, rather than making an assumption based on their appearance or voice. AAUW National uses they/them for individuals in writing when their pronouns are unknown.As an organization we need to create a space where non-binary, gender-fluid and transgender individuals feel comfortable and want to participate. Fighting gender discrimination is at the heart of our mission and shouldn’t be perpetuated within our own organization. We must learn to be welcoming and include different perspectives into what we do.

See also:

They Pronouns: https://www.mypronouns.org/they-them