The ingredients of medicines are often divided into active ingredients and excipients. Put simply, excipients are all the ingredients other than the active ingredient!
I love the word excipients.
We very often see use of the word filler - which is somewhat misleading. A filler is an excipient with a specific function - it adds bulk. Calling them all fillers is somewhat misleading. Other functions of excipients include:
Antiadherents
Binders
Coatings
Colours
Disintegrants
Flavors
Glidants
Lubricants
Preservatives
Sorbents
Sweeteners
Vehicles
Some excipients have multiple functions.
The word filler often seems to imply that the substance is being used instead of the active ingredient - to reduce the amount of active ingredient. But we'd better remember that some of these excipients are absolutely essential.
The article linked below might be of interest: