Writing utensil that uses graphite (commonly referred to as lead). Regular pencils usually have a graphite shaft surrounded by wood. Also available in a mechanical version where the graphite length can be adjusted and sharpening is not needed.
(geometry) A family of geometric objects with a common property, such as the set of lines that pass through a given point in a projective plane.
(optics) An aggregate or collection of rays of light, especially when diverging from, or converging to, a point.
