The words "well regulated militia" appear in the preamble to the second amendment. Some believe that this preamble somehow waters down the right to keep and bear arms. "Well regulated" means "trained". "militia" means all men of fighting age. Hence, any male who is trained in the use of firearms is part of the well regulated militia, and is entitled to keep and bear arms. Nowadays we tend to include women as well, so the only requirement to keep and bear arms is to be well trained in their use.