A burin is a highly refined tool used by Homo sapiens in the Upper Paleolithic industry (though earlier example have been found, it was not until this time that they became abundant). Burins were used for gouging and engraving bones, antlers and wood. It was a precision tool, often used to make smaller tools, such as needles. The tool itself was generally made from flint and derived from flakes or blades. Burins are commonly found on tools with combined functions.
How To Make A Burin
Truncation Burin
First, using pressure (pressing force to remove extra material from a stone core) or percussion flaking, a flake or blade is prepared. The end point of the flake or blade is then removed by truncation retouch (resulting in a flat edge which is at a right angle to the sides). The last step is the removal of a “burin spall” (a thin, elongated sliver of stone) by striking one side of the truncated edge. The removal of the spall gives the burin a small, sharp cutting edge (called a facet, or negative scar) on one side of the tool.
Dihedral Burin
The preparation of this type of burin also begins with the preparation of a flake or blade. Then a small platform is chipped off of one end point. This platform will serve as a striking surface. The final step is the removal of a spall from either side of the platform. The burin facets combine to form a sharp point.
A micro-burin looks like a miniature burin, but is not an actual tool. Rather, it is a byproduct of the manufacture of a microlith.
Sources:
http://www.hf.uio.no/iakk/roger/lithic/spectech.html#anchor241258
http://imnh.isu.edu/stonetool/resources/glossary/glossaryab.html