What is yuri? As explained on the Yuricon website:
Yuri can be used to describe any anime or manga series (or other thing, i.e., fan fiction, film, etc.) that shows intense emotional connection, romantic love or physical desire between women. Yuri is not a genre confined by the gender or age of the audience, but by the *perception* of the audience. We can, if we want to, differentiate between shounen yuri - written by men for a primarily male audience; shoujo yuri - written by women for a primarily female audience and; what we at Yuricon like to think of as "pure" yuri - written by lesbians for a lesbian audience...but it's still all yuri.
In short, yuri is any story with women in love (or lust) with other women.
Manga are Japanese comic books, translated to English for the American and other English speaking markets. Therefore, yuri manga are Japanese comics with the theme of lesbian love.
For lovers of yuri manga, there’s a new book out titled Yuri Monogatari 6, published by ALC Publishing, the only all-yuri publisher in the world. Erica Friedman is the President of Yuricon and its publishing arm, ALC Publishing. Erica also runs the yuri anime and manga blog Okazu.
Yuri Monogatari is an annual collection of “lesbian-themed Japanese-style comics.” You’ll find works by Rica Takashima, Eriko Tadeno, J. D. Glass (who I was fortunate enough to meet during a reading in New York) and more. Yuri Monogatari 6 is available now at the Yuricon website and Amazon.
In addition, Erica is offering a way to get Yuri Monogatari 6 for free. Details at Project Engage.