One meter (1 m) is defined as 1/299,792,458 of a light-second, a standard that helps establish other SI units. Weight can be measured in Newtons, slug, and pound-force, with 4.448 Newtons equating to one pound-force. It's important to distinguish between mass and force, as slugs are a unit of mass while Newtons and pound-forces measure force. A Newton is defined as the force needed to accelerate one kilogram at one meter per second squared. Understanding these definitions is crucial for accurate engineering calculations.