The slug is a unit of mass associated with Imperial units. It is a mass that accelerates by 1 ft/s^{2} when a force of one poundforce (lbf) is exerted on it. Therefore a slug has a mass of 32.17405 poundmass or 14.5939 kg.^{[1]}
(in terms of mass x acceleration) as
The slug is part of a subset of coherent units known as the gravitational footpoundsecond system (FPS), one of several such specialized systems of mechanical units developed in the late 19th and the 20th century. See the article poundal for an explanation of the problem such English units were introduced to solve.
The slug was first used in 1902 by Arthur Mason Worthington (1852–1916) in Dynamics of Rotation (OED), but it didn't see any significant use until decades later. A 1928 textbook says: "No name has yet been given to the unit of mass and, in fact, as we have developed the theory of dynamics no name is necessary. Whenever the mass, m, appears in our formulae, we substitute the ratio of the convenient forceacceleration pair (w/g), and measure the mass in lbs. per ft./sec.^{2} or in grams per cm./sec.^{2}".^{[2]}
Another name for this unit in early literature is the geepound.^{[3]}
The unit slinch (derived from the words sluginch ^{[4]}) is an inch version of the slug (1 slinch = 1 lb_{f}·s^{2}/in = 12 slugs).^{[5]} The unit blob (bl) is also an inch version of the slug (1 lb_{f}·s^{2}/in).^{[6]}
System  Gravitational  Engineering  Absolute  

Force (F)  F = m·a  F = m·a/g_{c} = w·a/g  F = m·a  
Weight (w)  w = m·g  w = m·g/g_{c} ≈ m  w = m·g  
Units  English  Metric  English  Metric  English  Metric 
Acceleration (a)  ft/s^{2}  m/s^{2}  ft/s^{2}  m/s^{2}  ft/s^{2}  m/s^{2} 
Mass (m)  slug  hyl  poundmass  kilogram  pound  kilogram 
Force (F)  pound  kilopond  poundforce  kilopond  poundal  newton 
Source: Mechanical Measurements^{[7]}
