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:
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: