blackboard

Etymology

From black + board, because such surfaces were once typically made of black slate.

noun

1. A large flat surface, finished with black slate or a similar material, that can be written upon with chalk and subsequently erased; a chalkboard.
   Drawings and pictures are more than mere ornaments in scientific discourse. Blackboard sketches, geological maps, diagrams of molecular structure, astronomical photographs, MRI images, the many varieties of statistical charts and graphs: These pictorial devices are indispensable tools for presenting evidence, for explaining a theory, for telling a story. 2012-03, Brian Hayes, “Pixels or Perish”, in American Scientist, volume 100, number 2, archived from the original on 2013-02-19, page 106

verb

1. To use a blackboard to assist in an informal discussion.