It stands for lesbian, gay, bisexual and transgender, however most of the time people use it to include any sexuality that is not heterosexual. Basically it's a community for non-straight people.
Lesbian gay bisexual transgender. It is attraction to opposite sex, and any feelings suggesting আপনি are in the wrong sex's body. (Personally, there are some things the এলজিবিটি গোষ্ঠী community involves despite it being hetero)