Short answer: "men of the fisc" usually means serfs attached to the royal demesne; their main counterpart in many sources are the "men of the benefice" (holders of benefices or fiefs) — i.e., free tenants and vassals who owed service rather than unfree labor.
Now the fuller picture, step by step:
- Top: Monarch / Crown
The king (or duke/count) stood at the top and held the ultimate authority and large tracts of land (the fisc or royal demesne).
- Great lords / Tenants-in-chief (barons, magnates)
These were the principal noble landholders who held land directly from the ruler, owed military and council service, and in turn granted land to others.
- Mesne lords, knights, and vassals
Those who held fiefs from greater lords. Their relationship was personal (fealty and military/service obligations). They were generally free (not serfs).
- Free peasants / copyholders / tenants
Free rural inhabitants who held land by rent or fixed service and kept legal personal freedom. In some regions they had considerable rights.
- Villeins / unfree tenants / serfs (men of the fisc)
"Men of the fisc" typically refers to people bound to the crown's land (fisc) or the demesne — effectively serfs who owed labor services, dues, and were tied to the land. They had limited legal rights and could not freely leave the manor without permission.
- Slaves (earlier periods or specific regions)
In some areas and earlier times fully enslaved people existed; over most of medieval western Europe slavery declined and serfdom became the predominant unfree status.
- Clergy (parallel hierarchy)
Higher clergy (bishops, abbots) could be great landholders and sit with magnates; parish priests and monks were integrated into local social structures but formed a distinct estate with its own rights and obligations.
- Townspeople / burghers / merchants
Urban classes with charters, trades, and guilds. Their legal status often differed from rural classes and could allow mobility and privileges.
Key differences and obligations — quick guide:
- Free vassals/tenants: held land in exchange for military/service obligations and owed personal loyalty (fealty).
- Serfs/men of the fisc: tied to the lord's land, owed labor (weekwork, harvest services), payments in kind, and were subject to manorial jurisdiction.
- Clergy: separate legal privileges, could be powerful landowners or local pastors with modest means.
Important caveats:
- Terms and precise statuses varied by time and place (Carolingian, Norman, later medieval England, France, etc.).
- "Men of the fisc" is a term often found in royal/administrative contexts (people attached to the royal fisc); similar categories exist under other names in local sources.
- The system changed: serfdom could weaken or strengthen locally; towns offered avenues of freedom; legal reforms altered rights over centuries.
If you want, I can give a compact mnemonic, a region-specific chart (e.g., 11th-century England: king → tenants-in-chief → knights/mesne lords → free men → villeins → serfs), or primary-source examples (Domesday Book entries or Carolingian capitularies) to illustrate these categories.