A more thorough explanation:

Definition: Decimae rectoriae is a term used in Ecclesiastical law to refer to the fixed tithes payable to the parson of a parish. These tithes are also known as parsonage tithes and cannot be lost by prescription.

For example, if a farmer in a parish has a crop yield of 100 bushels of wheat, he would be required to give 10 bushels of wheat to the parson of the parish as decimae rectoriae.

Another example would be if a parishioner sells a cow, they would be required to give 10% of the sale price to the parson as decimae rectoriae.

These examples illustrate how decimae rectoriae were a fixed percentage of certain goods or income that were required to be given to the parson of a parish.