setup time (tsu)

The time interval between the application of a signal at a specified input terminal and a subsequent active transition at another specified input terminal.

NOTE 1 The setup time is the actual time interval between two signal events and is determined by the system in which the digital circuit operates. A minimum value is specified that is the shortest interval for which correct operation of the digital circuit is to be expected.

NOTE 2 The setup time may have a negative value, in which case the minimum limit defines the longest interval (between the active transition and the application of the other signal) for which correct operation of the digital circuit is to be expected.

References: 

JESD99B, 5/07
JESD100-B, 12/99