What does "transition of glideslope intercept waypoint" mean in the 737 FCOM?
As a generic (non-737 specific) answer, it means that when the Flight Director is armed to capture an ILS glideslope, the VNAV flight director mode, being a vertical path based on baro altitude, is cancelled once the aircraft passes through a waypoint that the RNAV system calculates to be the geographical intercept point of the ILS glideslope beam (the intercept waypoint) because the Flight Director is expected to capture and track the ILS glideslope and RNAV/VNAV guidance is no longer required.