In the present Imperial House Law, it refers to sons of the Imperial family who are in the direct line and in the three or more degree of kinship from the emperor (not in collateral line and counted from the emperor who is a direct ancestor).
現行の皇室典範では、天皇から直系で三親等以上離れた皇族男子を指す（傍系でなく直系尊属の天皇から数える）。