A burr grinder uses flat or conical burrs to grind coffee beans when brewing coffee. One burr stays still while the other burr spins around while grinding the coffee beans. The burrs grind the coffee to a more consistent size than a blade grinder because 1. the burrs only grind a few coffee beans at a time and 2. the amount of space for ground coffee to fall through is determined by the size setting you choose on the grinder. All baristas will tell you that the most important factor in brewing high quality specialty coffee is a good burr grinder because it helps give you an even extraction.