The Krusty Krab Semi-Annual Charity Night was a made-up event set up by Mr. Krabs in the episode "Penny Foolish." It is semi-annual, meaning it is scheduled to take place again sometime in the future.
Role in episode
Mr. Krabs thinks that SpongeBob found a penny. Desperate for it, he makes several costly and futile attempts to convince SpongeBob to give it to him.
During the night of that day, Mr. Krabs invites SpongeBob to a fancy movie and restaurant (only a fancy version of the Krusty Krab) for the Krusty-Krab Semi-Annual Charity Night. At the Charity Night, Krabs shows SpongeBob a film about being "penniless." SpongeBob states that he would like to donate a penny if he had one. Mr. Krabs screams in horror inside his shell.