A sound effect associated with Akemi Homura from Mahou Shoujo Madoka Magica, it is a play off her name. Homura's nickname among Japanese fans is Homuhomu. This phrase was never used in the drama, though.
A certain phrase written with Madoka runes appeared in the Episode 3 and made this meme well known: "Watashi wa Homuhomu ha desu (I'm in the Homuhomu sect)."