An Albaster is a Fae who feeds off sexual shame.
"Saskia" told Bo that Albasters are the natural enemies of Succubi, because while succubi feed off and create sexual pleasure, Albasters do the same except with sexual shame. They make women feel guilty about their sexual behavior. The guilt spirals into eating disorders and ultimately suicide.
When Bo confronted Bertram, the Albaster, he accused her of "asking for it" by pulling "a whore's trick at the bar". He called his victims "bitches" and told her that none of them "were innocent" because all of them gave in to desires of the flesh.
Saskia attacked and overpowered the Albaster by turning the tables on him with sexual seduction.
When Saskia chi-drained him, she identified him as Dark Fae and "one of my own clan."
- 1.10 The Mourning After