Cullet is one of the oldest terms in glassmaking and is waste or scrap glass. Due to the difficulties of starting the melt of the glass metal cullet is often added to trigger the process. Some studios use only cullet to save on raw material costs.
French is Groisil
German is Scherben
Italian is Rottame di vetro
Czech is Strepy
Frit is the finely ground coloured glass used for colouring the melt or adding to a worked piece by marvering or other methods. This US glass supplier also uses the term so it is common to English speaking countries http://www.system96.com/Pages/Frit.html
Corning defines this further: Batch ingredients such as sand and alkali, which have been partially reacted by heating, but not completely melted. After cooling, frit is ground to a powder and melted. Fritting (or sintering) is the process of making frit.
Any other uses of these terms is likely to be erroneous and likely as not born in a poorly editted book for collectors. Other uses of these two words should be avoided to prevent further confusion.
Corning also provided the word for unwanted inclusions in glass as SCALE.Scale
An accidental inclusion in glass, consisting of corrosion products detached from the metal implements used to stir the batch or to form the object.
I have heard various other terms for this over the years, perhaps others would comment.
Kevin has also added the terms provided by Glass Technologist Adam Dodds "Stones"& "Salts".
Frit could also appear and of course will be a small piece of coloured glass in the wrong place.
Fritting (or sintering) is the process of making frit.