The starter file (.rft) chosen when creating a new Family in the Family Editor, which pre-configures its hosting behavior and category - distinct from a Project Template (.rte), which sets up an entire new project. Picking "Door" as a family template pre-wires wall-hosting behavior and standard door parameters, while picking "Generic Model face-based" sets up something that can attach to any surface - choosing the wrong family template at the start is one of the most common reasons a custom family behaves unexpectedly later.