Single Sword: The sword in one hand.
We use the term "single sword" to refer generally to all methods of fighting using a sword in one hand only. Fighting using a shield or other defensive objects is so different from fighting with a single sword alone that we will talk about that in another section.
Single swords have been documented all the way into antiquity. They were used as a primary weapon but also as a sidearm. From the Roman gladius and Celtic leaf blades through the viking era, medieval times, all the way through to the 20th century, single swords were used.
Despite their ubiquity, there are no manuals as far as I know for the arming swords of medieval times. The earliest sword manual comes from the 1300s and is specific to the sword used with a small shield called a buckler.
There are manuals on the use of the messer and some discussing the use of falchion which are both large machete like single edged blades from the medieval era. In the 1500's, George Silver wrote Paradoxes of Defence and Brief Instructions on my Paradoxes of Defence. There are Bolognese manuals on cut and thrust swords as well.
We use George Silver as a basis for teaching single sword because of the emphasis that Silver places on timing and distancing and because it hails back to an older style of fighting...a style prior to the advent of basket hilts and rapiers, swords specialized for the thrust.