Plain English Meaning
When the part of the ILS that gives you up-and-down guidance to the runway isn't working, you can still fly the approach using only the side-to-side guidance, but you have to stay higher and need better visibility to land.
Full Definition
The higher landing minimums published on an Instrument Landing System (ILS) approach chart that apply when the glideslope component is unusable or out of service. With no glideslope guidance available, the approach reverts to a non-precision localizer-only approach, which uses a higher minimum descent altitude (MDA) instead of a decision altitude (DA) and typically requires greater visibility.