Malossol is a Russian word that quite literally translates to "little salt". It is often used to describe caviar as sturgeon roe must be treated with salt in order to become caviar.
Originally, the term Malossol was used to distinguish higher grade caviar from ordinary caviar. When caviar was being produced more than two hundred years ago, preservatives didn't exist to properly conserve and extend the shelf-life of caviar. The only solution was to add salt, however if too much salt was added it overwhelmed the taste and quality of the caviar, compromised the cell walls of the roe and caused the caviar to lose its characteristic "pop".
Thus, the term "Malossol" was born, to inform both buyers and sellers that the caviar had not been overly salted (between 3-5%) and was of the highest quality and taste.
Today however, Malossol is no longer indicative of a caviar's grade, quality, or indeed origin - all caviar is treated with salt in order to properly preserve the roe and add to its taste.