Void-of-course Moon
The stretch after the Moon's last exact aspect in a sign, before it enters the next. With nothing left to complete, tradition reads these hours as poor for launching and fine for finishing.
Moving through a sign, the Moon completes a sequence of exact aspects to the other planets. Once it has made the last one it will manage before leaving the sign, it runs void of course: still moving, but with no more appointments until the next sign. A void period can last minutes or the better part of a day, and it ends the moment the Moon makes its ingress.
The idea comes from horary astrology, where a void Moon traditionally meant that nothing would come of the matter asked about. Popular practice translates that into scheduling advice: a weak hour for launches, signings, and openings, a perfectly good one for finishing, sorting, and resting. Hold it lightly; it is a nuance, not a law.
Definitions vary between traditions, mostly over which bodies and aspects count. Ours is the common modern one: the last exact conjunction, sextile, square, trine, or opposition to any planet from the Sun through Pluto, the same aspect set used everywhere else on this site. The Moon calendar lists each window alongside the aspect that closed it.