Final answer:
In a decision structure, the action is conditionally executed and occurs only if a specific condition evaluates to true, as seen in programming constructs like if statements.
Step-by-step explanation:
In a decision structure, the action is conditionally executed because it is performed only when a specific condition is true. A decision structure can also be referred to as a control structure, a conditional statement, or an if-then statement. In programming languages such as Python, Java, and C++, this structure is used to execute a block of code only if a particular test evaluates to true.
An example of a decision structure in programming is the if statement. If the condition within the if statement is true, then the actions or statements within its block will be executed. If the condition is false, the program will skip the block of code and continue with the rest of the program.