Its rector is really a parish priest, having all the essential rights of such a dignity, but still bound to defer in certain matters to the pastor of the mother church.
The marks of deference required are not so fixed that local custom may not change them.
This term is also applied to churches established within the limits of an extensive parish, without any dismemberment of the parochial territory.
In practice, however, the curates of such filial churches act as parish priests for their districts, although by canon law the dependence upon the pastor of the mother church remains of obligation, though all outward manifestation of subjection has ceased.
In the union of two parishes in the manner called "union by subjection", the less important of the parish churches may sink into a condition scarcely distinguishable from that of a filial church and be comprehended under this term.