Plain English Meaning
A runway with an instrument approach that tells you where to line up left-to-right, but not how steeply to come down. You handle the descent yourself using published altitudes at certain points along the approach.
Full Definition
A runway equipped with an instrument approach procedure that provides horizontal (lateral) guidance to the runway but does not provide electronic vertical (glide path) guidance. Pilots use it during approaches that rely on lateral navigation aids such as VOR, NDB, LOC, or LNAV, where descent is managed by stepping down to published minimum altitudes rather than following an electronic glide slope.