Cell characterization
Beginner
Measuring each building block in a library, by careful computer simulation, so the design tools know how fast it is and how much power it uses.
Novice
Running circuit simulations of every standard cell over a grid of input transition times and output loads, at each process, voltage and temperature corner, and storing the measured delays, transitions, power and timing checks in Liberty files.
Expert
Automated SPICE runs on the extracted cell netlist: function recognition, arc enumeration, delay and slew at fixed thresholds, internal power, leakage per state, pin capacitance, and setup/hold/min-pulse-width bisection. Grid choice and thresholds decide how accurate the interpolated tables are; libraries are re-characterized whenever models or layouts change.
Explained in From devices to a cell library (Transistors).
See also: Liberty (.lib), NLDM (non-linear delay model), SPICE.