Talking about a window in the cockpit that can be opened to see out of.
Not sure about light aircraft, but most airliners have them.
On DC9s for example, there is a CV window on each side that opens inwards and then slides back out of the way, this can be used to see forward if you cannot see through windscreen, also on the DC9 it is big enough to escape through, or as I have done many times open to clean the windscreen. (on the ground).
