Definition
GLIDESLOPE INTERCEPT ALTITUDE
The published minimum altitude to intercept the glideslope in the intermediate segment of an instrument approach. Government charts use the lightning bolt symbol to identify this intercept point. This intersection is called the Precise Final Approach fix (PFAF). ATC directs a higher altitude, the resultant intercept becomes the PFAF.
Source: FAA Pilot/Controller Glossary (verbatim from the Federal Aviation Regulations).