Defined by the fine folks at neutrois.com as "someone who identifies as being non-gendered and seeks to lose the major physical signifiers that indicate gender to others (breasts, facial and body hair, crotch bulges, etc)" - but neutrois, genderless, or neuter gender identity does not require physical changes or body dysphoria. Sometimes, genderless/neutrois people enjoy it when "children have trouble determining my gender" and make that their goal; other times, gender is less important to them - so unimportant that they identify with none. Neutrois folks make up an important part of the genderqueer/transgendered community.
These are some of the people who use non-gender-specific pronouns.