A "pencil mustache" is a narrow, thin mustache that resembles a line drawn with a pencil. It typically sits just above the upper lip and is often styled to be very precise and well-groomed. This type of mustache gained popularity in the early to mid-20th century and is often associated with classic Hollywood actors and characters. Famous figures like Clark Gable and Errol Flynn sported pencil mustaches, contributing to their iconic looks. The style can convey a sense of sophistication and charm, making it a timeless choice for those looking to enhance their facial features.