The definition of a tagboard is a type of sturdy cardboard.
An example of a tagboard is cardboard used for a poster or to post notes on.
sturdy cardboard used for tags, posters, mountings, etc.
A smooth-surfaced heavy paper or light cardboard used especially for making stencils, cutouts, and posters. Also called oak tag.
Origin of tagboardtag1 (perhaps because such paper or cardboard was used to make tags) + board.