poster board

or post·er·board

noun
  1. a thick, fairly stiff cardboard composed of layers of paper or paper pulp compressed together and typically used to support displays.
adjective
  1. of, relating to, or made of poster board.

Origin of poster board

First recorded in 1900–05
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018