Short answers, pulled from the story.
Yuri literally means "lily" in Japanese, a word also used as a feminine given name. In 1976, Ito Bungaku, editor of a gay men's magazine, used the term in reference to female readers in a letters column, and an association with lesbianism subsequently developed. By the mid-2000s, following the founding of specialized yuri manga magazines, the term was broadly recognized as a genre name for works depicting same-sex female intimacy.
Yuri became a discrete publishing genre following the founding of Yuri Shimai and Yuri Tengoku in 2003, the first manga magazines devoted exclusively to yuri. Comic Yuri Hime launched in July 2005 as a successor and established the market further. Before 2003, the term was used informally, primarily within dojinshi fan culture.
Class S is an early twentieth century Japanese literary genre depicting intense but platonic same-sex bonds between schoolgirls, always destined to end with graduation, marriage, or death. Nobuko Yoshiya was among its pioneering authors. Critics variously describe Class S as a distinct genre from yuri, as a proto-yuri, or as a component of yuri, and many of its tropes carried forward into the genre.
The anime adaptation of Naoko Takeuchi's Sailor Moon, running from 1991 to 1997, introduced the first mainstream positive portrayal of a lesbian relationship through Sailor Uranus and Sailor Neptune. The series' international success made the pairing widely known and helped build a yuri dojinshi culture. Japanese yuri magazines later classified Sailor Moon as a "monumental work" of the genre, even though it was not conceived as yuri.
Verena Maser's 2011 study of 1,352 Japanese yuri fans found 52.4% were women and 46.1% were men, with 69% of all respondents between 16 and 25 years old. A 2008 Ichijinsha study found women made up 73% of Comic Yuri Hime readers. As of 2017, the overall reader ratio of men to women was estimated at roughly 6:4.
Unlike boys' love, which targets a female audience, and gay manga, which targets gay male readers, yuri does not inherently target a single gender demographic. Yuri originated as a genre for female audiences but has also produced works aimed at male readers, as in Comic Yuri Hime S. Yuri also generally avoids graphic sexual content; sexual acts are rarely more explicit than kissing, in contrast to the more explicit conventions of boys' love and yaoi.