Your answer is only a Google search away (BTW, you forgot the link to the used hardware). The wiki page for your display explains everything.
I've searched a lot on google and of course the answer I wanted wasn't there.
There is only explained what pin goes to BUSY, not the meaning of the BUSY line.
That's why I stayed as general as possible, not linking anything.
The busy signal is an output which tells the microcontroller that the display is busy and cannot react to commands....
This is a part of the answer I was looking for, the other part is if the pin should be some specific digital/analog one etc..
The type of the signal and what pin I cannot use for BUSY line.
An ESP32 board is not an Arduino, so the connections have to be adapted if you use an ESP board.
I know what they are since I have both, my question wasn't about how to connect a specific display to a specific board but the display was only an example.
The question was on BUSY line generically, for a display, a keyboard or whatever.