Transition time (slew)
Beginner
How quickly a signal flips from 0 to 1, or from 1 to 0. A sharp edge flips fast; a slow edge flips gradually.
Novice
The time a signal takes to swing between two set fractions of the supply voltage, for example from 20% to 80%. The input transition is one of the two numbers used to look up a cell’s delay; the output transition becomes the next cell’s input transition.
Expert
Measured between the library’s slew thresholds (slew_lower/upper_threshold_pct) and scaled by slew_derate_from_library. In SKY130 hd these are 20% and 80% with a derate of 1, so a 10 ps index is a 16.7 ps full-swing ramp. STA propagates slew along every path; max_transition caps it.
Explained in From devices to a cell library (Transistors).
See also: NLDM (non-linear delay model), Load capacitance.