It's a common phrase used to express surprise, confusion, or curiosity about something that just happened or was said.
For example:
* "¡Que fue eso!" (What was that!) after a loud noise.
* "¿Que fue eso que dijiste?" (What was that you said?) when someone said something unclear.
The phrase can be used in a variety of contexts and can express different emotions depending on the tone of voice.