The love that dare not speak its name is a phrase from the poem "Two Loves" by Lord Alfred Douglas, published in 1894. It was mentioned at Oscar Wilde's gross indecency trial and is usually interpreted as a euphemism for homosexuality (although Wilde denied that it was).
In Wilde's definition, "the love that dare not speak its name" was:
Some authors have suggested that this quotation referred to pederasty rather than to male homosexuality in general.
References
The love that dare not speak its name Wikipedia(Text) CC BY-SA