The tiny middle class: Burghers

Burghers are free citizens, usually living in towns or cities. They usually don’t own land, or they simply own a building. They differ from peasants in that they usually have specialized skills. They ply their trades and they pay their taxes, usually in the form of coins rather than goods or produce like peasants.  Some lords use tolls and fees to indirectly tax their burghers rather than tax them directly or in addition to taxing them directly.
Sometimes unskilled laborers in urban areas or highly skilled peasants blur the line between peasant and burgher. Just think of burghers as the tiny middle class in a medieval society.
Scarterra has proportionally more burghers than real word medieval Europe.
Besides the normal skilled crafts needed for a medieval era society to function, a lot of burghers work in industries that support adventurers alchemy, collecting and processing reagents, and other rare trades. Lords and ladies also need to dip into the adventurer economy so they can maintain retainers capable of helping them with magic and monsters.