Magnam Opus

The Latin meaning for "Great Work". Usually meaning the greatest, most popular, pinnacle, or most renowned achievement of an artist, artist or composer. Or a "masterpiece"

Albiet in the case of George R.R. Martin, this refers to a big fat lazy and stinky turd (sometimes whistling in the wind for at least 8 years).

George R.R. Martin choked on a roasted water chestnut and died, leaving his Magnam Opus in his undergarments.