What is the defining feature of a local variable?

The defining feature of a local variable is that it can only be used within the expression that defines it. This encapsulation makes local variables particularly useful for keeping calculations and data manipulation self-contained, aiding in the clarity and modularity of the code. Since local variables are temporary and exist solely in the context of the expression or function where they are declared, they help prevent unintended interference with other parts of the application.

This feature ensures that the data stored in a local variable is not accessible outside its scope, which is important for managing state and avoiding conflicts with other variables. By allowing the developer to define a variable that can be used for computations without affecting global or shared variables, local variables enhance the control and organization of data within specific logic or functions.

The other choices do not accurately represent the nature of local variables. For example, local variables cannot be passed into a process model, called from any interface, or directly save data to a database, as these functionalities pertain more to variable types or actions that exist beyond the local scope context.