sheet of slate; for writing with chalk
"The teacher turned to the blackboard and began drawing a complex geometric diagram with fresh pieces of chalk."
A large flat surface, finished with black slate or a similar material, that can be written upon with chalk and subsequently erased; a chalkboard.
"The teacher turned to the old blackboard at the front of the room to write out today's math problems in white chalk."
To use a blackboard to assist in an informal discussion.
"During our brainstorming session, we used the blackboard to quickly sketch out ideas before moving on to the next topic."