Plain English Meaning

The altitude shown on the approach chart where you should be flying level when the glideslope needle comes alive and starts guiding you down toward the runway.

Full Definition

The published minimum altitude at which an aircraft on an ILS or similar precision approach is expected to intercept the glideslope from below while flying inbound on the localizer. It is depicted on the instrument approach chart by a lightning-bolt symbol on the profile view and represents the lowest altitude the pilot may descend to before glideslope capture.

Context Anchor

Seen on instrument approach charts during that provide vertical guidance to a runway.