Vtoss is a term that is only used in Category A procedures; it is used establish the Take-Off Distance Required. The definition of TODRH is:
The horizontal distance required from the start of the take-off to the point at which VTOSS, a selected height and a positive climb gradient are achieved, following failure of the critical engine being recognized at TDP, the remaining engines operating within approved operating limits.
Note.— The selected height stated above is to be determined with reference to either:
a) the take-off surface; or
b) a level defined by the highest obstacle in the take-off distance required.
The minimum climb performance required at Vtoss is 100ft/min.
Jim