The Moon changes sign roughly every two and a half days. After making its last major aspect in one sign and before entering the next, it is said to be void of course. These periods can last minutes or more than a day.
Traditionally, matters begun during a void Moon 'come to nothing' — not disaster, simply no result. Horary and electional astrologers have used the rule for centuries.
In practice, void periods suit routine work, rest, reflection and finishing tasks rather than launching new ones. If an important meeting falls in one, it may wander or need to be repeated.
There are exceptions. Classical sources considered the Moon less hampered when void in Taurus, Cancer, Sagittarius or Pisces, signs where it is comfortable.
Do not let a calendar of void hours rule life. Many good things happen during them. They are most useful when choosing between flexible options, such as a launch date or the moment to send an important proposal.
Treat the void Moon as a breath between sentences: a moment to pause before the next theme begins.