"Super soldier" is a catch-all term referring to individuals who have been optimized for combat by various means. A "super soldier" can typically outfight several regular soldiers. Super soldiers usually have superior weapons and equipment. The idea originates with the Spartan warrior caste.
Note that to qualify as "super soldiers", a given soldier or unit of soldiers must substantially exceed the fighting capabilities of "rank and file" soldiers in the setting before equipment is taken into account.
Creating super-soldiers in fiction will typically involve some combination of the following:
- Creation of a hereditary warrior caste
- Genetic engineering
- Cybernetic modification
- Performance enhancing drugs
- Psychological conditioning
- An extraordinarily difficult and rigorous training program
- Recruiting or conscripting individuals who already have superhuman attributes
Their are numerous flaws in most super soldier programs in fiction. The most notable is diminishing returns: as the training duration extends, you reach a point at which additional training adds relatively little to combat effectiveness. Long training times also mean slow replacement of losses; even the most elite soldier can fall victim to a regular soldier getting a lucky shot.