a : a substance added to a product (as to increase bulk, weight, viscosity, opacity, or strength)
b : a composition used to fill the pores and grain especially of a wood surface before painting or varnishing
c : a piece used to cover or fill in a space between two parts of a structure
d : tobacco used to form the core of a cigar
e : material used to fill extra space in a column or page of a newspaper or magazine or to increase the size of a work (such as a book)
f : a pack of paper for a loose-leaf notebook
g : a sound, word, or phrase (such as "you know?") used to fill pauses in speaking