In 1855, Whitman's poetry collection Leaves of Grass appeared. The title was a play on words - "grass" was a slang term for the silly, informal pieces that compositors like Whitman would set in type when things got slow at work.
Whitman celebrated the human body with a frankness not seen elsewhere in American popular culture at the time - at least not in the respectable, church-going aspects of popular culture. His poems like "I Sing the Body Electric" embraced the human body in all its parts, even those covered up by clothes. He wrote about women's sexuality, and he also wrote frankly about sexual relationships between men. Whitman was gay (though he wouldn't have used words like "gay" in his lifetime) and wrote about erotic love between men in his poems with joyful fearlessness.