Sexuality is just one of the ways that people differ from one another. The term "sexual diversity" is often used in the context of sexual orientation. Not all people are heterosexual. Some people are gay, lesbian, bisexual, queer, or questioning.
Sexual diversity means that everyone has different understandings about what sexuality means to them. In the past, sexual diversity within the general population was less apparent and visible than it is today.
Over time, society today has become a lot more tolerant and accepting of the differences between people along the lines of religion, disability, ethnicity, race, and sexuality. This includes a recognition that in today's world we are a diverse community with respect to sexual orientation, gender identity, transgenderism, transsexualism, and intersexuality.
Although the term "sexual diversity" can apply to many different aspects of sexuality, it is usually defined as sexual orientation and/or gender identity. The document Sexuality Definitions defines many other sexuality terms, including acronyms and their meanings, that you may come across on SexualDiversity.org - and in everyday life.
The original rainbow flag, called the Freedom Flag, was devised by Gilbert Baker in 1978. The design has undergone several revisions since its debut with 8 colored stripes, and today the most common variant consists of 6 stripes: red, orange, yellow, green, blue, and violet.