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In the religion and mythology of Peru, Ecuador, and Bolivia, apus are the spirits of the mountains - and sometimes solitary rocks and caves, that protect the local people in the highlands. The term dates back to the Inca Empire.
Meanings of Apu
The word " a poo" has several possible meanings, depending on context
In fictional literature
According to one science-fiction novel, the natives know of extraterrestrials that claim to come from the planet Apu. Apparently they wish to keep this a secret, but the Apunians wish humanity to know all about them what this implies. An extract from this book, written by Vlado Kapetanovic;
"The stranger was silent for a moment, and then smiled at me and said: “We come from a planet we call APU, located outside the Milky Way Galaxy. We are protectors of the cells and the life. For this we are traveling through space to aid by different modes the planetary beings, but not to impress with the result that you believe in our existence and ‘extraordinary powers’” 
Other Apus in Bolivia and Peru are: Akamari, Antikuna, Chachani, Kimsa Chata, Illampu, Lady of Illimani, Machu Picchu, Pitusiray, Phutuq K'usi, Qullqipunku, Sinaqara, Tunupa, Willka Wiqi (Wakay Willka), Wamanrasu, Wayna Pikchu and Yanantin.
- Stevens, Wendelle; (2012-12-30). UFO CONTACT FROM PLANET APU Kindle Edition.