Definition & Meaning of "when two Sundays meet"

What is the origin of the idiom "when two Sundays meet" and when to use it?

The phrase "when two Sundays meet" is an idiom that signifies an event that is incredibly rare or virtually impossible. The origin of this phrase is not precisely documented, but it likely evolved from the idea that two Sundays can never occur back-to-back in the same week, emphasizing the extreme improbability of the mentioned event.