In the medieval era, a precaria was a grant of the use of church lands for the lifetime of the grantee, in return for a service rendered to the church. Such grants were, as the origins of this word imply, precarious in nature; the user held the grant at the will of the church, and the church could withdraw permission to use the land. Such grants are sometimes referred to as fiefs, although this is not technically correct because the land was owned and granted by the church, not by a lord.
Over the course of the medieval era, the church gained control over substantial tracts of land, and it used the precaria grant system to its advantage. Warriors might receive lands in exchange for military protection, while lords could essentially lease lands under such grants, providing payments for the church in exchange for the right to use the land. The user had to remain in good standing with the church to retain the land, and thus the church held a high degree of control.
However, the benefits to this arrangement were not all on the side of the church. The king could compel the church to grant lands, and it would have no choice but to obey, whether the order was issued as a suggestion or an outright demand. Kings could award particularly plum pieces of real estate to their favored followers through the church, without having to lose any of the lands they controlled. The church, in granting the precaria, would lose the right to any revenues from the land, even if it had been depending on them to finance ecclesiastical operations.
While the term of the land use usually extended through the life of the holder, sometimes a precaria would last for a shorter period of time, such as five years. Some ecclesiastical officials recommended this change in policy to make the forced precaria less appealing to the monarch; few loyal followers would want to be rewarded with the right to use land for only five years, with no guarantee of being able to continue using it after that point. This diluted the usefulness of forced land grants from the king's point of view, and allowed the church more autonomy over the disposition of its lands.
Land ownership during the medieval era was a complicated topic. Many people held lands only for the duration of their lifetimes and did not have the power to grant lands or the right to use them to survivors. This sometimes created situations where wives and children were left effectively penniless because their family wealth originated in revenues from lands held for the duration of the lord's life only.