An Equal Time Point is a point on the ETOPS route segment which is located at the same flying time (considering wind and temperature conditions) from the two associated suitable en-route Alternates.
The location of the ETPs is usually defined by the Operational Flight Plan (OFP) but can be also assessed by locating the mid-points (equal-distance points) on a plotting chart or orientation chart and by applying a wind correction (e.g. using the equal- time number method or a wind correction scale).
For fuel calculation these points (ETPs and PTOs) are covered by the calculation tool of the OFP.
Source: ICAO Annex 6