The big-step operational semantics of a graph is an operational semantics given by a set of reduction rules on an AST or other intermediate representation after syntactic analysis. Each reduction defines the largest size step that can be taken from an abstract machine state to the next state that follows a given model.
The small step semantics for the same language should coincide periodically.
Each reduction rule either defines a single reduction, or adapts a reduction by embedding the redex in a larger expression.
For example, see page 3 of this https://groups.seas.harvard.edu/courses/cs152/2021sp/lectures/lec02-smallstep.pdf
This contrasts Small-step operational semantics