Definition
The descent altitude and visibility values published on an ILS approach chart that apply when only the localizer (lateral guidance) is used, without glideslope (vertical) guidance. Because the approach becomes non-precision in this case, the minimum descent altitude is higher and the required visibility is typically greater than the full ILS minimums shown on the same chart.
Plain English
The lowest altitude and visibility you're allowed to use on an ILS approach when the glideslope isn't working or isn't being used, so you're flying with side-to-side guidance only.
Context Anchor
Seen on instrument approach charts, especially when the vertical guidance for an approach is unavailable or when the procedure is flown as a localizer-only approach.
Derivation
Localizer comes from localize, meaning to place or locate. In aviation, the localizer helps place the airplane left or right of the runway centerline. Minimum comes from a Latin word meaning smallest, which fits because these are the lowest allowed conditions for that type of approach.
Why Pilots Care
Sets the safe limit for descent and the point at which a missed approach must be initiated if the runway is not in sight.
Intuition Check
Minimums does not mean a rough suggestion or a comfort level here. It means the published legal and safety limit for altitude and visibility on that approach.
Example Sentence 1
When the glideslope flag appeared on final, the crew briefed and flew to the localizer minimums instead of the ILS minimums.
Example Sentence 2
With the glide slope out of service, the crew flew the approach down to the localizer minimums.