These abbreviations all refer to groups of people, which each letter representing a single or multiple group.
Some letters refer to sexual orientation—who someone is sexually and/or romantically attracted to—and some letters refer to gender identity—a person’s internal sense of being male, female, both, or neither.
All of the abbreviations refer to groups of people who in some way fall outside the most common norms of gender and sexual identity.
The L means “lesbian,” a lesbian being a woman who is romantically and/or sexually attracted to other women.
The G means “gay.” Gay can describe anyone who is romantically and/or sexually attracted to people of their same sex, or it can be used narrowly to describe a man who is romantically and/or sexually attracted to other men.
The B means “bisexual,” which can have two distinct meanings. Bisexual can describe someone who is romantically and/or sexually attracted to people of their own sex as well as people of the opposite sex, or it can describe people who are romantically and/or sexually attracted to people of their same gender identity as well as people of other gender identities. [Reminder: someone’s gender identity is their internal sense of being male, female, some combination of male and female, or neither male nor female.] In this second meaning, bisexual covers the same semantic territory as the word pansexual, but there are people who identify as one but not the other, and people who identify as both.
The T means “transgender,” which describes someone whose gender identity is different from the sex the person had or were identified as having at birth. Often, transgender means specifically that the person’s gender identity—their internal sense of their gender—is opposite the sex they had or were identified as having at birth.
The I means “intersex,” and describes someone born with intersexuality, a condition in which someone has both male and female gonadal tissue, or has the gonads of one sex and external genitalia that is either ambiguous or is of the other sex.
The Q can mean either “queer” or “questioning (one’s sexual or gender identity).” The second meaning is transparent: someone who is actively working to figure out what their internal sense of self is, or what kinds of people they’re romantically and/or sexually attracted to, falls under the Q of LGBTQ in its “questioning” meaning. The “queer” meaning of Q is broad: it can describe someone whose gender identity doesn’t match the sex they were identified as having at birth, or whose gender identity is not accurately characterized as being solely male or solely female; it can describe someone whose sexual and/or romantic attraction is not limited to members of a particular gender identity or sexual orientation; it can describe someone whose sexual orientation is not straight/heterosexual. Note that in LGBTQQ and LGBTQQIA there is a Q for each meaning. More on queer below.
The A means “asexual/aromantic/agender,” which addresses three different categories of people. Someone who is asexual doesn’t experience sexual desire or attraction; the person may experience romantic feelings. Someone who is aromantic (often shortened to aro) experiences little or no romantic desire or attraction; the person may experience sexual attraction/desire. Someone who is agender has an internal sense of being neither male nor female, nor some combination of male and female; the person’s gender identity is genderless, or neutral. Whether someone is agender has no relationship to who they’re attracted to; agender is a term of gender identity, not of sexual orientation.
The + means “others.” It denotes whatever gender identities and sexual orientations aren’t adequately covered by the other letters.