filler

a  : a substance that is added to a product to increase its size or weight

b  : material that is used to fill holes and cracks in a surface

c  : extra material that is added to something (such as a newspaper page or a recording) to fill space that would otherwise be empty

[count] : a sound, word, or phrase (such as “um” or “you know?”) that people say during a pause when they are speaking