An older medium for writing stuff on. They come in many colours, grey, green, black, brown. You can write on them using chalk, which is just a solid stick of something, which when rubbed, gives off pigmented dust. They are commonly used in classrooms, lectures, and meetings. However more and more of them are being replaced by Dry Erase boards, or white boards.

They generally come clean with a special eraser, which just smears the dust around and takes most of it off, however every so often (depending on use) it needs to be wiped down with a wet rag or sponge to get rid of the excess dust.

As much as i like white boards (having asthma and all, dust bad), there is still something about seeing a complex equation or proof take shape on a chalk board by someone who is really smart.