I believe it is shorthand for Molybdenum-Disulfide. A specialty lubricant. It is particularly important where the faces of two gears actually slide laterally against each other. The lubricant membrane between the two metallic surfaces undergoes a particular stress known as shear stress. Most oil and grease will not hold up to shear forces. Moly does. These particular forces are created in the Guzzi rear drive where the helical pinion shaft teeth slide along and over the ring or crown gear teeth. Such forces do not exist to any great extent within the engine or the transmission. Only within the final drive.
There are numerous products on the market. I have a small bottle of Power Punch from Moto International in Seattle. Should last me for years in the small quantities normally used.