frame-live-p

frame-live-p is a built-in function in `C source code'.

(frame-live-p OBJECT)

Return non-nil if OBJECT is a frame which has not been deleted.
Value is nil if OBJECT is not a live frame. If object is a live
frame, the return value indicates what sort of terminal device it is
displayed on. See the documentation of `framep' for possible
return values.