Believe it or not ICAO actually has a document for that! It's called "phase of flight definitions"
This document describes the final approach sub-phase (as part of the IFR approach phase) as ending when the flare begins. Alternatively the missed approach phase may be commenced at any time during the approach. The approach phase begins at the IAF.
Various other entities may have other definitions geared to how they are used. Most of them would seem to be applicable to statistical or accident reporting.
Here's another one:
Airplane Flight Manuals include landing distance tables which describe the landing distance as being from a point 50' above the runway threshold until reaching a complete stop.
I'm sure there must be more...
westhawk