Basic Definitions

Sexual orientation and gender identity (SOGI)

Sexual Orientation

Describes to whom a person is sexually attracted. Some people are attracted to people of a particular gender; others are attracted to people of more than one gender. Some are not attracted to anyone.

Affectional orientation is a term that describes to whom a person is romantically attracted, acknowledging that for many people there are more components to attraction than just sexual desire.

Asexual ~ not sexually attracted to anyone and/or no desire to act on attraction to anyone. Does not necessarily mean sexless. Asexual people sometimes do experience affectional (romantic) attraction.

Bisexual ~ attracted to people of one’s own gender and people of other gender(s). Two common misconceptions are that bisexual people are attracted to everyone and anyone, or that they just haven’t “decided.” Often referred to as “bi.” See also Pansexual and Queer.

Gay ~ generally refers to a man who is attracted to men. Sometimes refers to all people who are attracted to people of the same sex; sometimes “homosexual” is used for this also, although this term is seen by many today as a medical term that should be retired from common use.

Lesbian ~ a woman who is attracted to women. Sometimes also or alternately “same-gender-loving woman” or “woman loving woman.” See also Gay.

Pansexual ~ attracted to people regardless of gender. Sometimes also or alternately “omnisexual” or “polysexual.” See also Bisexual and Queer.

Questioning ~ a term used to describe someone who is unsure of or exploring their sexual orientation and/or gender identity.

Queer ~ a) attracted to people of many genders; b) self-identity label for people who feel they do not fit cultural norms for sexual orientation and/or gender identity; c) sometimes used as an umbrella term for all people with non-heterosexual sexual orientations; d) transgressive and challenging of the status quo; e) historically, a pejorative term – its use today is met with disfavor by some and worn proudly by others.

Straight ~ attracted to people of the “opposite” sex (see below); also sometimes generally used to refer to people whose sexualities a re societally normative. Alternately referred to as “heterosexual.”

Gender Identity and Expression

The ways, in which a person identifies and/or expresses their gender, including self-image, appearance, and embodiment of gender roles. One’s sex (e.g., male, female, intersex, etc.) is usually assigned at birth based on one’s physical biology. One’s gender (e.g., man, woman, genderqueer, etc.) is one’s internal sense of self and identity. One’s gender expression (e.g., masculine, feminine, androgynous, etc.) is how one embodies gender attributes, presentations, roles, and more. For more on gender identity and expression, please see Transgender 101:
 
Androgyny ~ the mixing of masculine and feminine gender expression or the lack of gender identification. The terms androgyne, agender, and neutrois are sometimes used by people who identify as genderless, non-gendered, beyond or between genders, or some combination thereof. See also Genderqueer.

Cross dresser ~ Cross-dressing refers to occasionally wearing clothing of the “opposite” gender, and someone who considers this integral part of his or her identity may identify as a cross dresser (note: the term Cross dresser is preferable to transvestite and neither may ever be used to describe a transsexual person).
Cross-dressing is not necessarily tied to erotic activity or sexual orientation.

Genderqueer / Third Gender / Gender Fluid / Two-Spirit ~ these terms are used by people who identify as being between and/or other than man or woman. They may feel they are neither, a little bit of both, or they may simply feel restricted by gender labels. Two spirits is derived from some Native North American cultures and can sometimes mean a mixture of masculine and feminine spirits in the same body.

Intersex ~ A general term used for a variety of genetic, hormonal, or anatomical conditions in which a person is born with a reproductive or sexual anatomy that doesn’t seem to fit the typical definitions of female or male. Some intersex individuals identify as transgender or gender variant; others do not. (Note: hermaphrodite is an obsolete term that is not currently considered appropriate.)

Transgender ~ First coined to distinguish gender benders with no desire for surgery or hormones from transsexuals, those who desired to legally and medically change their sex, more recently transgender and/or trans has become an umbrella term popularly used to refer to all people who transgress dominant conceptions of gender, or at least all who identify themselves as doing so. The definition continues to evolve.
 
Transsexual ~ the term transsexual has historically been used to refer to individuals who have medically and legally changed their sex, or who wish to do so. Most transsexual people feel a conflict between their gender identity and the sex they were assigned at birth. Other labels used within this group are MtF (male-to-female) or trans woman, and FtM (female-to-male) or trans man.

REFERENCE:
http://www.uua.org/documents/lgbtq/basic_definitions.pdf