"Slugthrower" is a colloquialism referring to projectile weapons that expel a slug or bullet (usually of metal) at high velocity. The most common form of such weapons are chemical firearms, which use the pressure wave of a small chemical explosion to accelerate a bullet within a confined barrel. Other forms of these devices accelerate the slug by other methods, such as compressed gas, linear magnetism, micro-rockets, and so forth.
The term "slugthrower" is usually used in a manner which implies personal weaponry, rather than larger artillery-grade examples.
A typical pistol had an effective range of 60 meters, while on a rifle this was extended to 300 meters. Sniper rifles had been known to pick off enemies from over a kilometer. Their firing rates varied immensely; some were single shot weapons, while others fired thousands of slugs a minute. Slugs also varied; some were made of metal, some ceramic or even hardened plastics. Ammunition for slugthrowers was often rarer than blaster gas, however, and thus more expensive. Varying calibers sometimes compounded this problem.
Slugthrowers were considered by many to be a primitive, inferior technology when compared to blasters, and were often used by those without access to better weapons, such as primitive cultures. However, they remained popular for the unique advantages they offered. For example, during the days of the Galactic Republic, mercenaries fearing an intervention by Jedi Knights used rapid-fire slugthrowers that were impossible to deflect, unlike blaster bolts. They were also popular amongst forces looking to take advantage of the explosive nature for intimidation or to ensure destruction. Whatever they lacked in functionality, they regained in stealth. A slugthrower could be silenced while a blaster could not. Also, blaster rounds were almost always visible. Although this could be seen as an advantage, non-tracer rounds used by slugthrowers added an extra element of confusion and surprise, not allowing the target to see where the shots were coming from. Furthermore, slugthrowers were generally cheaper and more easily repaired than blasters. In addition, the projectile itself could have unique properties. Explosive, incendiary and mercy slugs each had different effects. Explosive ammo dealt additional kinetic damage to a target. Incendiary ammunition could cause burns that were as dangerous as the projectile, or set items on fire. Mercy bullets made of rubber or semi-rigid plastic gave a way to set a slugthrower on 'stun'. Of course, this meant carrying extra ammo or magazines - and special rounds were costlier and rarer than conventional slugs. Bounty hunters that carried slugthrowers tended to make extensive use of special ammo in their work. Some mixed rounds in the same magazine, starting with mercy slugs and working their way up to more lethal types in case the less deadly projectiles failed to stop their opponents.
As blaster usage increased, the popularity of personal armor declined - while extremely effective against most slugs, even modern armor could not stop a direct blaster hit, and as a result the wearing of bulky or cumbersome protective gear seemed to offer little benefit, while still obstructing movement. Thus, the blaster arguably increased the usefulness of the slugthrower. 
Tatooine's Tusken Raiders used the Tusken Cycler as a long range weapon when they were not close enough to use gaderfii. Most Slugthrower projectiles could penetrate a Stormtrooper's helmet lens or vulnerable neck area, so when stormtroopers arrived on Tatooine, Tuskens often used them as target practice.
Several Rebel detachments carried slugthrowers, including Rebel SpecForce units, who preferred them because of the ability to silence them. Many used special explosive ammunition that was especially effective against stormtrooper armor. The Dressellians carried them at the Battle of Endor.
The term "slugthrower" is also used in other works of science fiction (such as Farscape) as a (usually somewhat pejorative) term for guns; the term is often, but not always, applied specifically to "primitive" gas-driven guns (using either compressed gas or chemical explosives) rather than electromagnetically-driven or other such "advanced" projectile weapons.