CallBack Function

Can someone give me a good definition of a Callback Function?

For example, the following just go through each window that is open.

Code:

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  Call EnumWindows(AddressOf AllWindows, 0)

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What is this one doing?

Code:

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  Call SetTimer(Form1.hwnd, int_ID, 500, AddressOf TimerProc)

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Thanks

It calls the TimerProc when (in this case) 500 milliseconds has past.
If you want more then one TimerProc (assosiated with the same form) you have to give them different IDs (the second argument).