What does the phrase "once upon a time" mean?
"Once upon a time" is a traditional opening phrase used in storytelling, particularly in fairy tales and fables. It means that the story being told happened in the past, often long ago, in a time not precisely defined. The phrase sets the stage for the introduction of the characters and the events of the story to follow.
Complete the following task based on the instruction and optional input provided.### Instruction:
What does the phrase "once upon a time" mean?

### Output:
"Once upon a time" is a traditional opening phrase used in storytelling, particularly in fairy tales and fables. It means that the story being told happened in the past, often long ago, in a time not precisely defined. The phrase sets the stage for the introduction of the characters and the events of the story to follow.