Final Answer:
Dynamic loading is b) Loading a routine only when it is called.
Step-by-step explanation:
Dynamic loading refers to the process of loading a software routine or module into memory only when it is called or required during program execution. This approach is in contrast to static loading, where all routines are loaded into memory at the program's start. With dynamic loading, the system loads modules on-demand, saving memory space and allowing for more efficient resource utilization. Option b correctly captures this definition by stating that dynamic loading involves loading a routine only when it is called during the program's execution.
Option B is the answer.