Wire-load model
Beginner
A rough guess at how long the wires will be, made before anything is actually laid out.
Novice
A table that guesses a wire’s length and electrical load from how many pins it connects to. Tools used it to estimate wire delay before any layout existed.
Expert
A statistical lookup, stored in older Liberty files, from fanout (the number of pins a net drives) to estimated capacitance and resistance. It predicts the average net well but individual nets badly, so the worst paths are mispredicted once wires dominate delay. Physical-aware synthesis replaces it with distances from a quick placement.