The word QI'lop (pronunciation: S) represents an important Klingon holiday (1). Do not confuse it with Empire Union Day. Although it was never confirmed, the word obviously is a compound noun, made of the words QI'military and lopcelebration, party.
Different spelling "Qetlop"
The word Qetlop is not canon, but has been created by members of the German Klingons fan group Khemorex Klinzhai. They use it for their biannual meeting. It was based on a misunderstanding of the word QI'lop, which was mispronounced by Michael Dorn as Qetlop on the audio tape Power klingon.
Phrases
There are several phrases which can be used during the celebration. As usual, one needs to pronounce them exactly as they are written (2).
Hoch DaSopbe'chugh batlh bIHeghbe'. Eat everything or you will die without honor.Ho'Du'lIjDaq to'baj 'uSHom lughoDlu'bogh tu'lu'. You have some stuffed to'baj legs in your teeth.juHwIjDaq Dochvetlh vItlhap. I will take that to my homematay'DI' vIHtaHbogh bIQ rur mu'qaDmey. Between us, curses run like water.reH 'uQvam vIqawtaH. I will remember this dinner forever.to'baj 'uS lughoDlu'bogh tIlaj. Accept these stuffed to'baj legs.