WordNet
n. an evening when members of a club or college can bring their friends as guests
Wikipedia
Guest Night was a British television programme which aired on the BBC from 1938 to 1939, with an additional set of episodes made in 1946. According to a contemporary account, it was similar to a radio programme called Men Talking. (see page 83 of PDF file).
The series was hosted by A.G. Street, with each episode featuring a meeting of guests from a particular field.
None of the episodes still exist, as methods to record live television were not developed until late 1947, and were used very rarely by the BBC until around the mid-1950s.
Usage examples of "guest night".
Captain John Reynolds, a particular butt of Cardigan's, was the centre of the notorious Black Bottle affair, in which his resignation was demanded because he was believed to have ordered a bottle of porter in the mess on guest night.
Dalby strode across to him in a paternal way, and led him to the table like guest night at Boodles.
He said, Were going to have a dinner guest night after next, Caroline.
Since it was a guest night, the table was set on both sides to accommodate the extra numbers, and many diners therefore sat with their backs to the rest of the hall.