noun
orbital period; period of revolution
Technical term in astronomy for the time a celestial body takes to complete one orbit around another.
地球の公転周期は約365日です。
The Earth's orbital period is about 365 days.
公転周期 is the orbital period (revolution around another body), while 自転周期 is the rotation period (spin around its own axis).
Compound of 公転 (revolution, orbiting) and 周期 (period, cycle).