Depending on the diocese, some bishops assign priests to parishes as "parochial administrators."
What is a parochial administrator?
Unlike a pastor, a parochial administrator has no specific term, and is not designed to be a permanent replacement.
In some cases, bishops will use this assignment as a test run to see if a priest fits well in a parish. Then often (usually one or two years later), that priest will be officially named pastor.
This method may seem strange to the laity, as the technical term doesn't sound very pastoral, but it is one way that bishops can manage their priests while serving the needs of parishes.