Facebook on Thursday started allowing users to self-identify as something other than male or female. Good. There may be some cynical ad-targeting motive at work, but as Facebook spokesman Will Hodges explains, "While to many this change may not mean much, for those it affects it means a great deal."

You can make the change in your Facebook settings, and choose who will (and won't) see your new gender nomenclature. You can also change the pronoun Facebook uses when it talks about you, to the gender-neutral (but grammatically problematic) "they" (not "xe" or "thon"). The new options are only available in the U.S. so far.

So, if you don't identify as male or female, then what? Well, Facebook offers 56 options. You can use up to 10 of them on your profile. Fifty-six sounds like a lot, but actually a lot of them are variations on a theme — "cisgender man" and "cisgender male," as well as "cis man" and "cis male." In terms of broad categories, there about a dozen. Here's a look at what they mean:

1. Agender/Neutrois — These terms are used by people who don't identify with any gender at all — they tend to either feel they have no gender or a neutral gender. Some use surgery and/or hormones to make their bodies conform to this gender neutrality.

2. Androgyne/Androgynous — Androgynes have both male and female gender characteristics and identify as a separate, third gender.

3. Bigender — Someone who is bigender identifies as male and female at different times. Whereas an androgyne has a single gender blending male and female, a bigender switches between the two.

4. Cis/Cisgender — Cisgender is essentially the opposite of transgender (cis- being Latin for "on this side of" versus trans-, "on the other side"). People who identify as cisgender are males or females whose gender aligns with their birth sex.

5. Female to Male/FTM — Someone who is transitioning from female to male, either physically (transsexual) or in terms of gender identity.

6. Gender Fluid — Like bigender people, the gender-fluid feel free to express both masculine and feminine characteristics at different times.

7. Gender Nonconforming/Variant — This is a broad category for people who don't act or behave according to the societal expectation for their sex. It includes cross-dressers and tomboys as well as the transgender.

8. Gender Questioning — This category is for people who are still trying to figure out where they fit on the axes of sex and gender.

9. Genderqueer — This is an umbrella term for all nonconforming gender identities. Most of the other identities in this list fall into the genderqueer category.

10. Intersex — This term refers to a person who was born with sexual anatomy, organs, or chromosomes that aren't entirely male or female. Intersex has largely replaced the term "hermaphrodite" for humans.

11. Male to Female/MTF — Someone who is transitioning from male to female, either physically (transsexual) or in terms of gender identity.

12. Neither — You understand this one: "I don't feel like I'm fully male or fully female. 'Nuff said."

13. Non-binary — People who identify as non-binary disregard the idea of a male and female dichotomy, or even a male-to-female continuum with androgyny in the middle. For them, gender is a complex idea that might fit better on a three-dimensional chart, or a multidimensional web.

14. Other — Like "neither," this is pretty self-explanatory. It can cover everything from "I'd prefer not to specify how I don't fit in the gender dichotomy" to "My gender is none of your damn business, Facebook."

15. Pangender — Pangender is similar to androgyny, in that the person identifies as a third gender with some combination of both male and female aspects, but it's a little more fluid. It can also be used as an inclusive term to signify "all genders."

16. Trans/Transgender — Transgender is a broad category that encompasses people who feel their gender is different than the sex they were born — gender dysphoria. They may or may not choose to physically transition from their birth sex to their experienced gender.

17. Transsexual — Transsexual refers to transgender people who outwardly identify as their experienced gender rather than their birth sex. Many, but not all, transsexuals are transitioning (or have transitioned) from male to female or female to male through hormone therapy and/or gender reassignment surgery.

18. Two-spirit — This term refers to gender-variant Native Americans. In more than 150 Native American tribes, people with "two spirits" — a term coined in the 1990s to replace the term "berdache" — were part of a widely accepted, often respected, category of gender-ambiguous men and women.