I think they mean a lunar orbit which is synchronized with the Moon's rotational period[0].
The Hill radius[1] for the Earth-Moon system is only 24,000 km. The orbital period for a satellite at this distance from the moon should be about 90 minutes. Increasing the distance to increase the period would put the object outside the Hill Radius, causing the satellite to eventually go into orbit around the Earth, rather than the Moon. So, it seems that lunar synchronous orbits do not exist, except at some lagrange stability points of the Earth-Moon system.
The Hill radius[1] for the Earth-Moon system is only 24,000 km. The orbital period for a satellite at this distance from the moon should be about 90 minutes. Increasing the distance to increase the period would put the object outside the Hill Radius, causing the satellite to eventually go into orbit around the Earth, rather than the Moon. So, it seems that lunar synchronous orbits do not exist, except at some lagrange stability points of the Earth-Moon system.
[0] https://en.wikipedia.org/wiki/Geosynchronous_orbit#Other_syn...
[1] https://en.wikipedia.org/wiki/Hill_sphere