Knapping is the shaping of rocks to form stone tools, strikers for flintlock firearms, or to produce flat-faced stones for building or facing walls, and flushwork decoration. In layman's terms it is a process of using hammer stones (which are nicely rounded hard stones), to slowly shape other stones to manufacture simple tools and other functional stonework. Shaping can mean creating sharp edges, flat faces or other shapes. Flint is a well known rock to work with, but other rocks like chert and obsidian can also be knapped.
There is a local flint knapping club in Davis. (Know about it? Edit this entry!)