I think you mean "Αόριστος" ("Aoristos")... It 's just like the simple past. It is used for actions that have happened in the past (began and have already ended) only for a moment. For example:
Ένιωσα σαν χαζός όταν την είδα. (Eniosa san hazos otan tin ida.) = I felt like an idiot when i saw her.