Plain English Meaning

It's the row on the approach chart that tells you how low you can descend, and how much visibility you need, when flying a full ILS approach straight in to the runway.

Full Definition

A line on an instrument approach chart showing the published minimums for a straight-in Instrument Landing System (ILS) approach to a specific runway. The 'S-ILS' line lists the Decision Altitude (DA) and required visibility for an aircraft flying the full ILS approach (using both localizer and glideslope) and landing straight ahead on the runway aligned with the approach.