Blackboard
来自Big Physics
wiktionary
From black + board, because such surfaces were once typically made of black slate.
etymonline
blackboard (n.)
"board painted black and written on in chalk," especially as used in schoolrooms, 1823, from black + board (n.1). Blackboard jungle "inner-city school rife with juvenile delinquency" is from Evan Hunter's novel title (1954).
