HOO meaning in Community ?

The Heroes of Olympus is a pentalogy of fantasy-adventure novels written by American author Rick Riordan. The novels detail a conflict between Greek demigods, Roman demigods, and Gaea (Roman name Terra) also known as Mother Earth. In the fourth book of the series, there is also a semi-large fight against Tartarus, which, in Greek mythology, was the darkest and deepest point of the underworld. The series can be a standalone volume, but is best to be read after Percy Jackson and the Olympians. The series made after the Heroes of Olympus timeline is The Trials Of Apollo. Riordan introduces Roman mythology in his sequel series as well as several new characters. The first book of the series, The Lost Hero, was published on October 12, 2010. The final entry in the series, The Blood of Olympus, was published on October 7, 2014.