a room in a school where lessons take place
"The teacher quickly swept up the broken glass from the classroom before the next lesson began."
A room, often in a school, where classes take place
"The teacher asked everyone to clean up their desks before leaving the classroom at the end of the day."
In plain English: A classroom is a room where students go to sit at desks and listen to their teacher during school hours.
"The teacher walked into the classroom to begin the lesson."
Usage: Use "classroom" to refer specifically to a room within a school or educational institution designed for teaching and learning activities. It does not apply to any generic space where instruction occurs outside of a formal school setting.
The word classroom is a straightforward combination of the words class and room that emerged to describe a space designated for instruction. It was formed by joining these two existing terms rather than evolving from an older root or undergoing a significant meaning shift.