Forward Pass and Backward Pass

There are two terms related to Critical Path that one may encounter. These are the terms Forward Pass and Backward Pass. These terms are related to ways of determining the early or late start [forward pass] or early or late finish [backward pass] for an activity. Forward pass is a technique to move forward through a diagram to calculate activity duration. Backward pass is its opposite. Early Start (ES) and Early Finish (EF) use the forward pass technique. (Source: https://press.teleinteractive.net/)