Visual Descent Point
AIM 5-4-3.f Approach Control
Visual Descent Points (VDPs) are being incorporated in nonprecision approach procedures. The VDP is a defined point on the final approach course of a nonprecision straight-in approach procedure from which normal descent from the MDA to the runway touchdown point may be commenced, provided visual reference required by 14 CFR Section 91.175(c)(3) is established. The VDP will normally be identified by DME on VOR and LOC procedures and by along-track distance to the next waypoint for RNAV procedures. The VDP is identified on the profile view of the approach chart by the symbol: V.
1. VDPs are intended to provide additional guidance where they are implemented. No special technique is required to fly a procedure with a VDP. The pilot should not descend below the MDA prior to reaching the VDP and acquiring the necessary visual reference.
2. Pilots not equipped to receive the VDP should fly the approach procedure as though no VDP had been provided.
If the visibility is less than the distance from the runway of the VDP, you won’t be able to make a straight-in approach and should prepare for a circle-to-land approach, if allowed.
Not all non-precision approaches have charted VDPs but you can easily calculate your own. The two most common methods for calculating a personal VDP result in a 3° glideslope:
Altitude to lose, in thousands of feet, times 3 equals the VDP in nautical miles.
I was going to write a detailed post on this topic but found this link while researching it. Glenn Carlson does it much better than I could and I have nothing to add.