Liberty (.lib)
Beginner
The catalog that tells the tool each building block’s size, speed and power use.
Novice
The text file that describes a cell library to the design tools: each cell’s logic function, its area, the electrical load of each input, tables of how its delay depends on conditions, and how much power it uses.
Expert
One file per corner (a combination of manufacturing process, supply voltage and temperature), often one per threshold-voltage flavor too. It holds lookup tables for delay, output transition and internal energy, timing checks such as flip-flop setup and hold, and limits such as max_transition and max_capacitance. Older flows also kept wire-load models here.
Explained in Logic synthesis (Design Flow).
See also: NLDM (non-linear delay model), Standard cell.