What is a callback function?

[Vivid_Void]

The title really says it all I am just wondering what a callback function is and how it works?

[Kampfkarren (boyned)]

Have you seen this thread, posted yesterday?

ELI5 on Callbacks

I’m trying to understand what callback functions are, but any explanation I search for here or elsewhere either goes over my head or doesn’t apply to lua. Could somebody explain callbacks and asynchronous vs synchronous in very simple terms?