For a long time, the public used terms like “gay” and “queer” to define everyone who wasn’t heterosexual (also referred to as "straight"). Now, it is common to use LGBT (or LGBTQ) instead.
LGBT is a broad acronym used in place of “gay”, “lesbian”, or “queer”. It is used to respectfully signify a whole group of people. The letters, LGBT, each refer to a different identifier. The L refers to Lesbian, which means a woman who is attracted to other women. The G refers to Gay, which means a man who is attracted to other men. Bisexual is identified with the B, and transgendered with the T. A bisexual is someone who is attracted to both genders, and a transgendered person is someone who feels they are another gender. When speaking about something that affects the entire queer group, the LGBT acronym is recommended. On the other hand, if just one group is being talked about, such as “gay men” or “lesbian women”, the LGBT acronym wouldn’t be used.
Why use LGBT instead of Gay?
Why use LGBT? LGBT is used because some issues are not specific to one group. For example, the issues of bisexual individuals are not always shared by gay and lesbian individuals. Transgendered individuals have entirely different issues than lesbians, gays, and bisexuals. Therefore, when describing the entire non-heterosexual group, use LGBT. If you wish to signify a specific group, as in Freedom from discrimination in the workplace does not apply just to gays or lesbians, for example; it applies to everyone who is non-heterosexual. Those who are transgendered don't want to be called gay any more than a Hoosier wants to be called a Buckeye!
What about LGBTQ?
The LGBTQ acronym encompasses those who don’t neatly fall under the LGBT banner, or for those who aren’t sure. (Q means both “questioning” and “queer”.) It is a respectful addition to the LGBT acronym, but isn’t as commonly used as LGBT.
Words NOT to use
Even today, people use the term “gay” as a pejorative, describing something undesirable or stupid. “That’s so gay”, is a common expression used to define how awful, stupid, or boring something is. There are terms not to use, and gay is one of them. Another term never to use is “homo”, and of course, the f-word. Don’t use them in this manner.
LGBT stands for "Lesbian Gay Bisexual and Transgendered". Sometimes LGBT is written as LGBTQ, or "Lesbian Gay Bisexual Transgendered and Queer/Questioning". When writing about the non-heterosexual community as a whole, it is always appropriate to use LGBT. To say “gay” when you really want to include everyone isn’t as respectful as it could be. LGBT is a catch-all term that can and should be used in writing. It is inappropriate to ever use a slang term like gay and use it to define something as undesirable. (As in, "That's so gay!") Be careful if you make a habit out of it, because the person you say it around may very well be a part of the LGBT community, and they will think less of you for it.